C- Book 01

FACULTY OF ENGINEERING TECHNOLOGY

OPEN UNIVERSITY OF SRI LANKA

DEPARTMENT OF MECHANICAL ENGINEERING DIPLOMA IN TECHNOLOGY – LEVEL 3 MEK3170 – C PROGRAMMING

BOOK 1 C PROGRAMMING

Author Ms. W. Sheranga Ayeshi Nanayakkara

Editor Mr. W. Hasala Peiris

Open University of Sri Lanka Nawala Nugegoda, Sri Lanka

First published in 2007

© 2007 Open University of Sri Lanka All rights reserved. No part of this course book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording or from any information stored in a retrieval system, without permission in writing from the Open University of Sri Lanka.

UNIT 1 Basics of programming

Session 1 Introduction to C++ Programming

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Session 2 C++ Data types and Variables

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Session 3 Basic Input Output & C++ Programming Techniques

24

Session 4 C++ Operators and Expressions

36

Session 5 C++ Control Structures

49

Session 6 More Control Structures

63

Session 7 Basics of Functions

75

Session 8

87

Arrays

Session 9 Pointers

102

Session 10 More on Functions and Strings

117

Session 1 Introduction to C++ Programming Contents Objectives Introduction 1.1 What is a programming language? 1.1.1 A brief history of programming languages 1.2 Programming in C++ 1.2.1 Characteristics of C++ 1.3 What is a programme? 1.4 Compiling and Executing a C++ programme 1.4.1 How to develop C++ programmes 1.4.2 A simple C++ programme 1.4.3 Program explanation 1.5 Compile errors 1.6 C++ Case sensitivity Summary

Objectives After reading this lesson you should be able to: ¾ Understand what is a programming language and the evolution of it ¾ The characteristics of a programming language ¾ What is a programme and what are the basic tasks of a programme ¾ How to enter, compile, link, and run a simple C++ program. ¾ Find out the compile errors in a simple C++ programme and correct them

Introduction In the fast moving world, almost in every activity computers are being used. Since we give instructions to computers by means of programmmes, developing programs have also become a vital part. In order to develop programs, programming languages are being used. Since the evolution of programming languages in 1940’s, different programming languages were developed to serve different purposes. Among them, C++ is one of the

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most popular programming languages and this book intends to cover most of the aspects of C++ programming. This session is an introductory session, which is designed to provide some background knowledge on programming. It also discusses the evolution of programming languages in brief and introduces C++, by emphasizing its characteristics and the importance of those characteristics. In addition, it is essential to know what is meant by a programme and the basic tasks of a programme in general. This session covers up the above information as well as step by step procedures needed to follow in order to develop a simple C++ programme. This session also helps to understand the common programming errors and how to locate them and correct them and run a programme successfully.

1.1 What is a Programming Language? A programming language is an artificial human-created language, which translates instructions from a human readable format to a computer readable format. It has become a main method of instructing a computer to perform specific tasks. Each language has its own special set of keywords and syntax, which makes each programming language unique.

1.1.1 A brief history of Programming Languages In 1946, a German Engineer called Konrad Zues, developed the first programming language called ‘Plankalkül’. However the world’s first commonly used programming language ‘Short Code’ was developed three years after that. Since then the innovation of programming languages began. In 1951, Grace Hopper began designing the world’s first compiler. In 1954, IBM began the development of FORTRAN. FORTRAN became the first commercial high level programming language. FORTRAN II was presented in 1958 with new features. COBOL (Common Business Oriented Language) was created in 1959, which is still used in many companies. Some of the programming languages like ALGOL 60, APL, SNOBOL, BASIC and Pascal appeared later. In 1972, Dennis Ritchie created the C-language and its documentation appeared after two years. Today the world has come a long way and we have very powerful programming languages like C++, Java with object oriented programming features.

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1.2 Programming in C++ C++ is an object-oriented programming (OOP) language, developed by Bjarne Stroustrup at Bell Labs during 1983-1985. It can be considered as an enhancement to the C programming language. Since C++ has absorbed features and concepts of more than forty years of language design, it has become an extremely powerful programming language. After the introduction of C++ in 1990, it has become one of the most popular commercial programming languages. It also runs on most computers, from PCs to the most powerful supercomputers and C++ is viewed by many as one of the best languages for creating large-scale applications.

1.2.1 Characteristics of C++ C++ has certain characteristics over other programming languages. The most remarkable ones are: ¾ Supports Object-oriented programming Object-oriented programming allows the programmer to design applications based on the concept of “objects” and interactions between them, simplifying the programming task. This makes it easier to solve larger and more complex problems. (Object oriented programming will be discussed in detail later in this book.) ¾ Generality Apart from the normal computation tasks, C++ can be used to develop databases, business applications as well as graphical applications. ¾ Portability A C++ code can be successfully compiled and run in almost any type of computing environment or operating system with or without minimum changes to the source code. ¾ Reusability C++ programs allow a greater re-usability of code. Therefore, new functionality can be added to the existing code with or without minimum changes to the original code. ¾ Modular programming A C++ application that has been made up of different individual components can be modified and maintained independent of the other components. So the whole application need not be compiled when making changes to a single component, saving programmer’s effort and time.

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¾ Concision Codes written in C++ are very short in comparison with other languages because of the use of special characters and keywords and this saves some effort of the programmer too. ¾ C Compatibility C++ is backward compatible with C language, which means a code written in C can easily be included in a C++ program without making any change. ¾ Speed The resulting code from a C++ compilation is very efficient and hence it produces efficient programs. ¾ Maintainability C++ programmes are easy to maintain. (e.g., when the business requirements change, the program can be extended and enhanced without a great expense.)

1.3 What is a Programme? A computer programme is a collection of instructions that describe a task or set of tasks to be carried out by a computer. Computer programs are normally designed for problems that would be difficult or impossible to solve by other ways or to solve a certain problem more efficiently and effectively. These programmes can be simple or very complex depending on the requirements. Programmes can be developed for straightforward calculations like adding two numbers or for more complicated problems like guiding a satellite into the right orbit and handling the transmission of data. Almost every programme performs 3 basic tasks in solving problems, irrespective of whether it is simple or more complex. 1. 2 3.

Manipulate data Perform operations Provide results

Manipulate Data Programs manipulate data by accepting data from inputs (e.g., keyboard), creating new data and storing them, or modifying existing data. There are two fundamental forms of data that are facilitated by the programming languages. ¾ Textual data – Characters and strings (e.g., A person’s name) ¾ Numerical data - numbers. (e.g., A persons age)

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In addition to these types of data, C++ facilitates more complex data types and these will be discussed in detail in the sessions to come. Perform Operations In order to produce results from data, operations are being used. Programming languages are used to give instructions to perform operations. A simple example of an instruction would be adding two numbers. Provide results After performing operations, results are generated and it can be information or data to another operation. It can be displayed on a screen, stored in databases, used to produce reports or it can be transmitted to another computer.

1.4 Compiling and Executing a C++ Programme C++ is considered as a high-level programming language. They are English-like and closer to human language, which is easy to read, write, and maintain. Since the computer can understand only the machine language, a programme that is written using C++ needs to be translated into the machine language before executing. This translation is performed by a very specialized computer program called a compiler. The programming code that is written is called the source code, hence for the compiler the input is the source code and the output is the machine code or object code. We can argue that the compiler translates the source code into an intermediary form, as the object code cannot be run in the computer. Therefore, we need another program called a linker, which is invoked by the compiler, in order to translate the object file into an executable program. Only an executable program can be run on the computer. Here, the compiled object file is also linked with a function library in order to produce the executable program. A library is a collection of linkable files, which can be linked to a programme. These libraries are supplied with the C++ compiler but a progammer can also create his own set of libraries to be linked with the programme.

1.4.1 How to develop C++ Programmes There are several tools available for developing C++ programs. These tools make developing easier and more productive. Currently, the tools given below are popular among them. C++ Builder by Borland Visual C++.NET by Microsoft

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You can use a specific tool or even a text editor like Windows Notepad or the DOS Edit command to write your source code. Source code is the series of C++ statements that you have written and it can be a single file or a combination of several text files.The text files has to be saved with the extension .cpp,.cp or .c and the source code has to be compiled using the compiler. For different compilers the compiling commands are different. So you have to use your compiling command according to the type of compiler you have. A successfully compiled programme produces the object file which has the .obj extension. Since the compiler invokes the linker, the programme is linked with the needed libraries and produces the executable file with the extension .exe. The diagram given below shows the steps involved in developing a C++ programme and the files that are involved in each operation.

Figure 1.1 - Compiling and running C++ programs In figure 1.1 the programmer can write the source code using any kind of a C++ editor and save the file. Here, the file is saved as Hello.cpp. When the programmer compiles the programme, it generates both the object file (hello.obj) and the executable file (hello.exe). When the programmer run the programme the executable file is loaded and executed.

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1.4.2 A simple C++ programme 1. 2. 3. 4. 5. 6. 7. 8.

#include #include void main() { clrscr(); cout<<"Open University, Nawala."; getch(); }

Output: Open University, Nawala. Note: Most of the programmes in this book contain line numbers on the left. These numbers are only for reference within the book and should not be included in your programme.

1.4.3 Programme Explanation ¾ #include #include tells the C++ compiler's preprocessor to include the iostream standard header file in the programme. The .h extension stands for the word 'header’. This iostream file includes the declarations of the basic standard input-output library in C++. We have included this file in our programme because its functionality is going to be used later in the programme ('iostream.h' is used for 'cout' operation) ¾ #include This is another header file used in C++ programming. ('conio.h' is used for the functions 'clrscr()' and 'getch) clrscr() - This is a function used for clearing the output screen. getch() - This will pause the program while the output window is visible until the user hits any key.(This is not a standard C++ feature. You have to use this feature if you are using Turbo, Borland C++) ¾ void main () In all C++ programs it is necessary to have a main function. Independently of its location within the source code, main function will always be the first one to be executed in any C++ program. A pair of parentheses (()) indicates a function declaration. Every function has a function name (e.g., main) and a pair of parentheses that follow its name.

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Curly braces ({}) shows the body of the main function. What is contained within these braces is what the function does when it is executed. (Here line 5,6 and 7 is the body of the main function which is contained within the braces in line 4 and 8) ¾ cout << " Open University, Nawala."; This line is a C++ statement. cout is declared in the iostream standard file which we have included at the beginning of the programme. This statement generates the visible effect that we can see as the output, ‘Open University, Nawala.’ ¾ Semicolon character (;) In line 5, 6 and 7 the statements ends with a semicolon character (;). This character is used to mark the end of the statement and it is essential to include this at the end of all expression statements in C++ programs.

1.5 Compile Errors Compile errors occur during the compilation process of a programme. Compile-time errors can occur either due to errors from the compiler itself or more likely syntax errors in the code. Nowadays new compilers highlight the errors in a programme, and also point out the exact place in the code where the mistake is. The programme given below shows a demonstration on compile errors. 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. cout << "Mechatronics Programme!\n"; 7. getch(); In the above programme the closing parenthesis ( }) of the main function is missing. Hence the compiler will generate a compile error like: Error Mechatronics.cpp, line 8: Compound statement missing } Mechatronics.cpp is the file name and it shows the line number and also the problem. Compiler assists in finding most of the common compile errors but sometimes the compiler finds it unable to report complex user errors. In addition, in every identified compile error it doesn’t show the correct line numbers. So it is the programmers responsibility to locate the errors and correct them.

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Activity 1.1 – Analyzing the tasks of functions This activity is intended to analyse the tasks and the importance of clrscr() and getch() functions, as they are used in every programme. First, type the above program into your editor, compile and execute it. 1. Remove the clrscr() function and recompile. Now run the programme several times and explore the output screen. 2. Remove the getch() function and recompile and run the programme. Observe the execution of the programme carefully.

1.6 C++ Case Sensitivity C++ is a case sensitive language. Hence, uppercase and lowercase letters are considered to be different. e.g., In declaring variable names the word ‘age’ is different from ‘Age’, which are different from ‘AGE’. (Variables will be discussed later in this book) Therefore, the programmer should be cautious about this factor and use correct uppercase and lowercase letters when writing C++ coding.

Activity 1.2 – Correcting errors in a programme This activity is intended to locate the compile errors that the C++ editor produces, and find the location and the nature of the error and correct them in order to provide an executable programme. First, type the program given below directly into your editor, exactly as shown and compile the programme. #include #include void main() { clrscr(); cout < "C++ Programming ----"; cout << " Session 1 ----; cout << " Second Programme!!!" getch(); }

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You will get number of compile error statements. Read the compilation errors carefully and fix the errors and run the programme.

Summary ¾ A programming language is an artificial, human-created language, which translates instructions from human readable format to a computer readable format. ¾ C++ supports Object-oriented programming. In addition Generality, Portability, Reusability, Maintainability, Efficiency are some of the characteristics of C++. ¾ A computer program is a collection of instructions that describe a task or set of tasks to be carried out by a computer. Every programme has 3 basic tasks. • Manipulate data • Perform Operations • Provide results

¾ To Create an executable C++ programme you should,

• Create a source code file, with a .CPP extension. • Compile the source code into a file with the .OBJ extension. • Link your OBJ file with any needed libraries to produce an executable program.

¾ Compile errors occur during the complication process in a programme. The programmer should locate them and correct them in order to successfully run the programme. ¾ C++ is case sensitive.

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Session 1 - Answers Activity 1.1 – Answer

1. The output of the programme will be printed without clearing the screen. Example: If you run the programme 3 time, the output will be Mechatronics Programme!Mechatronics Programme!Mechatronics Programme! 2. The output screen will be opened but will be closed immediately before waiting for you to press any key on the key board. Hence it is not possible to observe the programme output.

Activity 1.2 - Answer #include #include void main() { clrscr(); cout <<"C++ Programming ----"; cout <<" Session 1 ----"; cout <<" Second Programme!!!"; getch(); } Output: C++ Programming ---- Session 1 ---- Second Programme!!!

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Session 2 C++ Data types and Variables Contents Objectives Introduction 2.1 What are variables and data types? 2.1.1 Fundamental variable types in C++ 2.1.2 Declaration of variables 2.1.3 Assigning values to variables 2.1.4 Demonstration of the use of variables 2.2 C++ Constants 2.2.1 Literal constants 2.2.2 Symbolic constants. 2.2.3 Demonstration of the use of constants 2.3 Enumeration type 2.3.1 A Demonstration of the use of enumerations 2.4 The typedef keyword 2.4.1 A demonstration of the use of typedef keyword Summary

Objectives After reading this lesson you should be able to: ¾ Declare and define variables. ¾ Assign values to variables and to manipulate those values. ¾ Correctly use constants, enumerations and the typedef keyword in your programmes. ¾ Write the value of a variable to the screen.

Introduction In the previous session we developed a simple C++ programme which displayed a certain text. However, as you all know programmes are not limited only to printing simple texts on the screen. Programmes should be able to perform useful operations in order to produce valuable results. Hence in this session we introduce the concepts of ‘variables’ and ‘data types’ available in C++. 12

These variables are used to store data and retrieve them later in order to perform operations. This session also covers C++ basic data types and their technical details like their sizes and ranges. In addition, this session is also devoted to explain C++ constants. Both variables and constants offer various ways to represent and manipulate data in C++ applications. In developing these applications it is important to choose the proper data type in defining variables and constants. In addition, values should be assigned to the variables and constants according to their data types. Failing to do so will result in compile errors, unexpected and incorrect outputs and inefficient programmes. Hence this session provide guidance to take the right decision to choose the proper data types and to assign correct values to them.

2.1 What are Variables and Data Types? Programs need a way to store the data they use. Variables and data types are used for this purpose. Variable: Variable is a location in the computer’s memory, where information can be stored. After storing, these information can be retrieved and used later. Data type: In defining variables to store data first we have to define which type of data we want to store. The data type will have characteristics such as the range of values that can be stored and the operations that can be performed on variables of that type. In defining variables, each variable takes up a fixed amount of space in the computer’s memory.

2.1.1 Fundamental Variable types in C++ 1. Integer variables - Positive or negative whole numbers. Integer values come in three sizes. They are int, short int and long int. 2. Floating point variables - Floating point decimal numbers. There are in three sizes, float (single-precision), double (double-precision) and long double (extended-precision). 3. Character variables - Characters ( It can be a single letter, number, or a symbol) 4. Boolean Variables – Only hold a ‘true’ or ‘false’ value. (returns 0 when its false and returns 1 when its true) All the variables (except Boolean) can be divided into two types called signed and unsigned variables 1. Signed integers - either negative or positive. 2. Unsigned integers- always positive

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The table given below illustrates the data types used in C++ and their size and range. Name Description Size* Range* signed: -128 to 127 char Character or small integer. 1byte unsigned: 0 to 255 -32768 to 32767 Signed short Short Integer. 2bytes int/short int Unsigned short Unsigned short Integer. 2bytes 0 to 65535 int -2147483648 to 2147483647 Signed int Integer. 4bytes Unsigned int long int

Unsigned Integer.

4bytes

0 to 4294967295 -2147483648 to 2147483647

Long integer.

4bytes

Unsigned long int Unsigned Long integer. Boolean value. It can take one bool of two values: true or false. float Floating point number. Double precision floating point double number. Long double precision floating long double point number. wchar_t Wide character.

4bytes

0 to 4294967295

1byte

true or false

4bytes

3.4e +/- 38 (7 digits)

8bytes

1.7e +/- 308 (15 digits)

8bytes

1.7e +/- 308 (15 digits)

2bytes

1 wide character

Table 2.1-Data types used in C++ Note: The values of the columns ‘Size’ and ‘Range’ depend on the architecture of the system where the program is compiled and executed.

2.1.2 Declaration of variables In order to create a variable in C++, you must declare its type followed by the name of the variable. The variable type can be specified according to the type of data that are going to use in the programme. Variable names can be declared using any combination of letters, without any spaces between the letters. In general, meaningful and expressive names are being used in defining variable names in order to easily understand the flow of the program. Once the variables are declared they can be used within the rest of the program. Example 2.1: Suppose Mathematics marks of a student needs to be stored. In general, marks are positive values without decimal points. Hence the variable can be declared as below. int marks;

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Example 2.2: Suppose average mark of a student needs to be stored. As it can have a decimal value it can be declared as: float average; Example 2.3: Character variables can be used to store characters as shown below. char name; Example 2.4: In order to declare more than one variable of the same type, it can be declared as separate statements or in a single statement as shown below. In the three variables mark1, mark2 and mark3, marks of three subjects can be stored. int mark1; int mark2; int mark3; int mark1, mark2, mark3; Example 2.5: Variables without the word "unsigned" are assumed to be signed. Hence both declarations given below are the same. signed int mySalary; int mySalary; Example 2.6: An exception to this general rule is the char type, as we can declare variables to store even numeric values. Here it is necessary to use either signed or unsigned keyword in declaring char-sized variable. unsigned char total; signed char value; Example 2.7: In declaring short and long variables, we assume that short is equivalent to short int and long is equivalent to long int. Therefore, the declarations given below are equivalent: Short month; Short int month;

2.1.3 Assigning Values to Variables Depending on the data type of the variable, a value can be assigned to it using the assignment (=) operator. Variables can be defined and initialized separately or both steps can be done in one sentence. int age; age=25; or int age=25; ¾ Assigning values to integer variables. signed int salary = 25750; signed int temperature = -10; unsigned int start = 0; int width = 85; As integers comes in short and long values:

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short int lastValue = 175; long int Total = 25000; unsigned long bigValue = 22411; signed short smallValue= -5; ¾ Assigning values to float variables. float interestRate = 0.05; float calculation= -99.99 double fahrenheit = 99.876; long double Balance = 50899.90; ¾ Assigning values to char variables. When assigning a character to a char variable, it is enclosed within single quotes. char letter = 'k'; char user_input = '7'; As numeric values also can be assigned to variables of character type: char value = 89; We can declare signed and unsigned characters as well. signed char firstValue = 110; signed char myKey = -25; unsigned char start = 500; Note: Plain ‘char’, is neither signed nor unsigned: ¾ Assigning values to Boolean variables. bool correct_name = false; bool password = true;

2.1.4 Demonstration of the use of variables 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. 7. 8. 9.

unsigned short int workDays=5; float workHours=8.5; float payRate=90.50; float weeklyPay=workDays*workHours*payRate;

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cout<<"Weekly pay = Rs "<<weeklyPay;

11. getch(); 12. }

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Output: Weekly pay = Rs 3846.25

Activity 2.1- Working with variables Using a suitable variable declaration, write a programme which calculates the area of a triangle and displays the following output. Area of the Triangle is 27.5 Use the data and the formula given below in writing your programme: Height of the triangle is11 and the base of the triangle is 5. Area = 0.5 * height * base

2.2 C++ Constants Like variables, constants are data storage locations, but once a value is being initialized to a constant it cannot be changed later in the programme. There are two types of constants in C++ named literal and symbolic.

2.2.1 Literal Constants A literal constant is a value typed directly into the program. e.g., int age =25; Here, age is assigned to value 25 and it is a constant fix value. In the variable age the value will be always 25. Hence it s a literal constant.

2.2.2 Symbolic Constants. A symbolic constant is a constant that is represented by a name, just like variables are represented. But, once a symbolic constant is assigned it cannot be changed. After assigning a value to a constant in a programme, it cannot be reassigned. If you try to do so the compiler gives an error message. There are two ways to declare a symbolic constant in C++ using the #define keyword and the const keyword.

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¾ #define keyword Example: #define maximum 20; Note that the variable ‘maximum’ doesn’t have a specific type (int, float or char etc) ¾ const keyword In defining a constant with the use of ‘const’ keywork, a type needs to be specified. Example: const int FUTURE = 2025; This is a better way to define constants and it makes it easier to maintain the code as well as it prevents errors that can happen.

2.2.3 Demonstration of the use of Constants 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. const int FUTURE = 2025; 7. int year_of_birth, age_in_2025; 8. 9. 10. 11.

cout<<"Enter your year of birth:"; cin>>year_of_birth; age_in_2025 = FUTURE - year_of_birth; cout<<"\nIn 2025 you will be "<
12. getch(); 13. } Output:

Enter your year of birth: 1990 In 2025 you will be 35 years old.

The main advantage in using symbolic constants is, if a certain value needs to be changed, it can be done efficiently and effectively as there’s no need to make a change in every place that the value is being used. Example: Suppose in the above programme that you need to calculate your age in 2050. Here if you change the constant to const int FUTURE = 2050, it will be effective though out the whole programme. This is more effective in larger programmes where the programmers do not have to go through all the coding thus saving time and minimizing errors that can occur. 18

2.3 Enumeration Type Enumeration is a user defined variable type that enables the user to define values for the type. Enumerations are declared using the enum key word followed by the enumeration name. An enumeration value has to be included inside curly braces. Example: enum working day {Monday, Tuesday, Wednesday, Thursday, Friday}; Every enumeration has an integer value. The default starts with 0 and the rest will count up from there. Monday has a value of 0, Tuesday has the value 1 Wednesday has the value 1 etc. A value can also be initialized to an enumeration. Example: enum workingday { Monday=50, Tuesday, Wednesday=88, thursday, Friday=900 }; Here : Monday=50, Tuesday=51, Wednesday=88, Thursday=89, Friday=900 Note: enumerator variables actually are of type unsigned int.

2.3.1 A Demonstration of the use of Enumerations #include #include void main() { clrscr(); enum cards{ spades=5, hearts, clubs=10, diamonds }; cout<<"Spades value:"<<spades<<endl; cout<<"Hearts Value:"<
In the above programme, when ‘spades’ is assigned to 5, the next value is automatically assigned to 6. When clubs is assigned to 10, Diamonds will be automatically assigned to 11.

2.4 The typedef keyword The typedef keyword enables to create a synonym for an existing data type. A typedef declaration contains the typedef keyword followed by a name in the position of a variable name. Example: typedef unsigned long int UNLONG

2.4.1 A demonstration of the use of typedef keyword #include #include 1. void main() 2. { 3. clrscr(); 4.

typedef unsigned short int USHORT;

5. 6. 7. 8.

USHORT val1 = 4; USHORT val2 = 688; USHORT val3 = 34; USHORT total = val1+val2+val3;

9.

cout << "Total of the values = " << total <<endl;

10. getch(); 11 } Output: Total of the values = 726 In the above example total of three values are being calculated. In line 4, USHORT creates a synonym for ‘unsigned short int’. This has reduced the tedious, repetitious writing ‘unsigned short int’ in line 5,6,7 and 8. This also reduces the user errors that can happen in writing the same words over again in the programme.

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Activity 2.2-Using ‘typedef’ and ‘Const’ keywords Rewrite the programme in Activity 2.1 using the typedef and const key words. Use the keyword typedef in declaring the height of the triangle and use the const key word in calculating the area. (0.5 should be defined as a symbolic constant)

Summary ¾ In C++, there are four main data types. They are int, float, char and double. ¾ We define variables stating its type followed by the name of the variable. Then values are assigned to those variables using the assign (=) operator. ¾ Constants are C++ data storage locations like variables, but once defined constant cannot be changed. There are two types of constants in C++ named, literal and symbolic. ¾ Enumeration is a user defined variable type that enables the user to define values for the type. ¾ The typedef keyword enables to create a synonym for an existing data type.

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Session 2 - Answers Activity 2.1 - Answer #include #include void main() { clrscr(); unsigned short int height,base; float area; height=11; base=5; area=0.5*height*base; cout<<"Area of the triangle is "<<area; getch(); } Output: Area of the triangle is 27.5

Activity 2.2 - Answer

#include #include void main() { clrscr(); typedefunsigned short int USHORT; const float fix =0.5; USHORT height,base; float area; height=11; base=5;

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area=fix*height*base; cout<<"Area of the triangle is "<<area; getch(); } Output: Area of the triangle is 27.5

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Session 3 Basic Input Output & C++ Programming Techniques Contents Objectives Introduction 3.1 Basic Input/Output 3.1.1 Basic Output 3.1.2 Basic Input 3.1.2 A demonstration of basic input and output 3.2 Special formatting characters 3.3 Whitespace 3.4 Finding the size of variable types 3.4.1 A demonstration of the ‘size of’ operator 3.5 Simple type conversions 3.5.1 Explicit type conversion 3.5.2 Implicit type conversion 3.5.3. A demonstration of the type conversions 3.6 C++ Comments 3.6.1 A demonstration of the use of C++ comments Summary

Objectives After reading this session you should be able to: ¾ Develop interactive programmes using basic input and output operations. ¾ Use special formatting characters and whitespace in your programmes. ¾ Find the size of any data item or type using the sizeof operator. ¾ Perform simple type conversions. ¾ Properly document a programme using C++ comments. ¾ Identify different types of keywords used in C++.

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Introduction Programs given as examples in the previous sessions provided very little interaction with the user. Using the standard input and output library (iostream), which we have already used, we will be able to interact more with the user by printing messages on the screen and getting the user's input from the keyboard. This session outlines these basic input and output operations used in C++. In C++, there are special formatting characters which help to increase the readability of a programme and it also assists in producing special effects in the programme like making an alert sound etc. Whitespace in C++ also helps to increase the readability and comments helps to properly document a programme. In the previous session, C++ data types were introduced stating their data type and size in bytes. The ‘sizeof’ operator introduced in this session assist in finding the size of these data types and even the size of any data item. In this session, we will also introduce simple type conversions which help in converting one data type to another.

3.1 Basic Input/Output Input and output operations are used to interact with the user. Using the standard input and output library called iostream, messages can be written on the screen and the user's input can be taken from the keyboard.

3.1.1 Basic output The cout operator is used to print messages and data to the standard output which is the screen. (cout operator was used in programming demonstrations in the previous sessions) The insertion operator (<<) may be used more than once in a single statement: cout << “Open University, “<< “Nawala, ”<<”Nugegoda.”; In the above example, the output will be printed in a single line. In order to print this in separate sentences, endl manipulator can be used to add a new line. cout <<” Open University,”<< endl; cout <<” Nawala,”<< endl; cout <<” Nugegoda.”<< endl; In using a string of characters, it is enclosed between double quotes. When it is not enclosed they are considered as variables names. cout<<x; //This prints the content of x where x is a variable cout<<”Value is ”<
3.1.2 Basic input The standard input device is usually the keyboard. The cin operator is used for inputting data from the keyboard. In using the cin operator it must be followed by a variable that will store the data that is going to be entered by the user. int number; cin>>number; In the above example, first statement declares int variable called number, and the second statement (cin) waits for an input from the keyboard. When the user enters an integer value while the programme is running, it will be stored in the variable called number. In defining variables for input, it is necessary to define the exact type of variables depending on the type of data that is going to input from the keyboard. e.g., If the input value needs to be a character, a char type variable should be declared.

3.1.2 A demonstration of basic input and output #include #include void main() { clrscr(); char name1,name2; unsigned int num1,num2,total; cout<<"Enter the first letter of a subject:"; cin>>name1; cout<<"Enter marks of subject "<>num1; cout<<"\nEnter the first letter of another subject:"; cin>>name2; cout<<"Enter marks of subject "<>num2; total=num1+num2; cout<<"\nThe total is "<
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Output: Enter the first letter of a subject: a Enter marks of subject a 60 Enter the first letter of another subject: b Enter marks of subject b 88 The total is 148

Activity 3.1 – Practicing Basic input and output operations Modify the programmes in Session 2 activity 2.2 (Calculating the area of a triangle) to ask the user to enter the height and the base of the triangle. Output should be as below: Enter the height of the triangle: Enter the base of the triangle: Area of the triangle is ---

3.2 Special formatting characters The backslash character (\) is used as an escape character, allowing a programmer to include characters that would normally have a special meaning for the compiler. A list of characters and their operations are given below. Sequence \n \r \t \v \b \f \a \' \" \? \\

Meaning newline carriage return tab vertical tab backspace form feed (page feed) alert (beep) single quote (') double quote (") question mark (?) backslash (\)

Table 3.1 – Special for matting Characters

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¾ These characters can be used in the programme by typing the backslash followed by the character in a cout statement. cout<<”\n”; //This means a new line (The cursor will prompt to the next line) ¾ They are also can be defined as char variables. char tabCharacter = `\t';

3.3 Whitespace Whitespace (tabs, spaces, and newlines) is generally ignored by the C++ compiler. x=2+y; The above statement is same as x =2 +y; Mainly we don’t write programmes as given above as it will reduce the readability. We can use white space to make the programs more readable and easy to maintain. cout<<”Value of the programme =”<
Activity 3.2 – Structuring a Programme Write a programme which produces the following output as a chart: “Subjects and Marks Chart” Subject A B C

Marks 45 67 90

Total

‘202’

User needs to be prompted to enter three subject names (single character) and their marks. The programme should calculate the total of the subjects and it should be displayed as shown above.

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Note: Subject and their marks need to be displayed first and total should be displayed in the given place with an alert only when the user presses any key in the keyboard. The screen (user interaction messages and user inputs) should be cleared when displaying the chart. Hint: Use special formatting characters, and white space to make the output more consistent. Use getch(),clrscr() functions in getting the expected output.

3.4 Finding the size of variable types As discussed in session-2 every data type has a size (in bytes) depending on the architecture of the computer. C++ provides a useful operator called ‘sizeof’ for calculating the size of any data item or type. It takes a single operand which may be a type name or an expression and returns the size of the data type in bytes.

3.4.1 A demonstration of the ‘sizeof’ operator #include #include void main() { clrscr(); cout<<"char size cout<<"short size cout<<"int size cout<<"long size cout<<"float size cout<<"double size

= "<<sizeof(char)<<"bytes\n"; = "<<sizeof(short)<<"bytes\n"; = "<<sizeof(int)<<"bytes\n"; = "<<sizeof(long)<<"bytes\n"; = "<<sizeof(float)<<"bytes\n"; = "<<sizeof(double)<<"bytes\n";

cout<<"2.77 size = "<<sizeof(2.77)<<"bytes\n"; cout<<"MECHATRONICS size= "<<sizeof("MECHATRONICS")<<"bytes\n"; getch(); }

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Output: char size short size int size long size float size double size 2.77 size MECHATRONICS size

= 1 bytes = 2 bytes = 2 bytes = 4 bytes = 4 bytes = 8 bytes = 8 bytes = 13 bytes

3.5 Simple type conversions Type conversion means changing an entity of one data type into another.

3.5.1 Explicit type conversion Explicit type conversion is a special programming instruction, which specifies what data type to treat a variable in a given expression. Here, the value of the data types can be converted (typecast) to any of the other types. int i = 10; float r = float(i); It can be also written as float r = (float)i; (int) 5.67 //convert 5.67 to an int. Then the value will be 5. (double) 5 //convert 5 to a double to give 5.0 (char) 122 //convert 122 to a char whose code is 122. (unsigned short) 5.67 //convert 5.67 to unsigned short. Then the value will be 5.

3.5.2 Implicit type conversion Implicit conversions do not require any operator. They are automatically performed by the compiler. short x=5; int y; y=x; In the above statement a type casting operator need not be specified. This is known as a standard conversion. C++ allows standard conversions between numerical types (short to int, int to float, double to int etc), and to type bool and from bool to numeric values. Some of these conversions may imply a loss of precision.

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This can also be used when values of different types are mixed in an expression as given below. double d=1; int i=10.5 i=i+d;

3.5.3. A demonstration of the type conversions 1 #include 2 #include 3 void main(){ 4 clrscr(); 5 float tax_amount; 6 tax_amount=2556.22; 7 tax_amount=(int)2556.22; 8 cout<<"\nTax Payable =Rs."<
3.6 C++ Comments C++ comments are used in order to properly document a programme, as it increases the readability. On the other hand when a programme is properly commented a programmer can understand the programme without much effort saving his time. In addition, it will be useful for the programme’s future references. A C++ comment starts with `//’ (Forward slashes) and goes till the end of the line. In order to comment on multiple lines, start the comments with /* and end the comments with */. The C++ compiler ignores any text in the same line after the ‘//’ and also ignores the text between /* and */.

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3.6.1 A demonstration of the use of C++ comments 1. #include 2. #include 3. void main(){ 4. clrscr(); 5. /*This programme calculates the area of a circle 6. when the user inputs the radius value. 7. Variable declaration*/ 8. int radius; 9. float area; 10. //Taking user input 11. cout<<"Enter radius value:"; 12. cin>>radius; 13. //Calculating the area value 14. area=3.14159*radius*radius; 15. cout<<"\nArea is:"<<area; 16. 17.

getch(); }

Output: Enter radius value: 12 Area is: 452.388947

3.7 C++ keywords Certain words are reserved by C++ for specific purposes and they are called keywords in C++. Every language has these reserved key words. asm auto case catch char class const cons_cast continue default delete do double dynamic_cast else enum explicit export extern false float for friend goto if inline int long mutable namespace new operator private protected public register reinterpret_cast return short signed sixeof static static_cast struct switch template this throw true try typedef typeid typename union unsigned using virtual void volatile wchar_t while Table 3.2 – C++ reserved key words

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Additionally, alternative representations for some operators are reserved words under some circumstances. Some of them are given below. and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq Compiler may also include some additional specific reserved keywords and it can differ in different compilers. Note: C++ keywords cannot be used as identifiers. (As variables, constants etc)

Summary ¾ Input output operations are used to interact with the user. The cout operator is used for standard output operations and the cin operator is used for standard input operations. ¾ Special formatting characters have a special meaning for the compiler. There are several formatting characters and each performs a different task. ¾ Whitespace (tabs, spaces, and newlines) are generally ignored by the C++ compiler. ¾ C++ provides a useful operator called ‘sizeof’ for calculating the size of any data item or type. ¾ Changing an entity of one data type into another is called ‘type conversion’. There are two basic types of type conversions called explicit and implicit. ¾ C++ comments are used in order to properly document a programme, as it increases the readability. It is a good programming technique to include comments in every programme.

¾

Some words are reserved in C++ as ‘keywords’ and they cannot be used as identifiers in programmes.

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Session 3 - Answers Activity 3.1- Answer #include #include void main() { clrscr(); typedefunsigned short int USHORT; const float fix =0.5; USHORT height,base; float area; cout<<"Enter the height of the triangle:"; cin>>height; cout<<"Enter the base of the triangle:"; cin>>base; area=fix*height*base; cout<<"Area of the triangle is "<<area; getch(); } Output: Area of the triangle is 27.5

Activity 3.2- Answer #include #include

void main() { clrscr(); char name1,name2,name3; unsigned int num1,num2,num3,total; cout<<"Enter the first letter of a subject 1:"; 34

cin>>name1; cout<<"Enter marks of "<>num1;

cout<<"\nEnter the first letter of subject 2:"; cin>>name2; cout<<"Enter marks of "<>num2; cout<<"\nEnter the first leter of subject 3:"; cin>>name3; cout<<"Enter Marks of "<>num3;

total=num1+num2+num3; clrscr(); cout<<"\n \"Subjects and Marks\"\n"; cout<<"\n\tSubject"<<"\tMarks\n"; cout<<"\n\t"<
“Subjects and Marks Chart” Subject A B C

Marks 45 67 90

Total

‘202’

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Session 4 C++ Operators and Expressions Contents Objectives Introduction 4. 1 Operators in C++ 4.1.1 Assignment Operator 4.1.2 A Demonstration of the use of assignment operator 4.1.3 Arithmetic Operators 4.1.4 Relational Operators 4.1.5 A demonstration of the use of the Relational operators 4.1.6 Logical Operators 4.1.7 A demonstration of the use of the Logical operators 4.1.8 Increment and Decrement Operators 4.1.9 A demonstration of the use of the decrement operators 4.1.10 Conditional (Ternary) Operator 4.2 Precedence of operators Summary

Objectives After reading this lesson you should be able to: ¾ Manipulate data using C++ operators. ¾ Evaluate expressions using precedence of operators.

Introduction In order to work with variables and constants and manipulate data, we need a way to operate with them. C++ provides ‘operators’ for this purpose and keyboard symbols are used to denote them. This session is designed to introduce different types of operators used and the different actions they perform on data. The most commonly used one is the assignment operator, which mainly deals with assigning values to variables. In addition, this session outlines arithmetic operators, which are the common mathematical operations found on a calculator. Logical

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calculations also can be performed using the logical operators. Furthermore, C++ provides relational operators mostly to compare different types of values in order to execute statements. In addition, there are special types of operators which are unique to most programming languages. They are called increment and decrement operators which helps in incrementing and decrementing a given value. Each operator is assigned a priority and this is called the ‘precedence of operators’ which is one of the most important aspects in working with different types of operators.

4. 1 Operators in C++ An operator is a symbol, which performs a certain action in a programme. The symbols are mostly made of signs that are available in all keyboards. The actions are performed using a certain value or values. Theses values are mostly variables or constants and are called operands. C++ provides operators for composing arithmetic, relational, logical, bitwise and conditional expressions. It also provides operators, which produce useful side effects such as assignment, increment and decrement.

4.1.1 Assignment Operator The assignment operator (=) assigns a value to a variable. (This has been used in the programme demonstrations given in the previous sessions). Assignment operator helps you to perform several operations on variables. ¾ This operator operates in a right-to-left rule: Example 1: a=b; Here b is assigned to the variable a, which means the right value is assigned to the left value and never the other way. ¾ This is useful even in assigning the same value to couple of variables. Example 2: x = y = z = 7; This expression is equal to x=7, y=7, z=7. ¾ Assignment operator in C++ can also be used as the right operand of another assignment operation. Example 3: x=3+( y=7) is equal to y=7; x= 3+ y

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4.1.2 A Demonstration of the use of assignment operator #include #include void main() { clrscr(); int a, b; x = 25; y = 10; x = y; y = 6; cout << "The value of x is "; cout << a; cout << " and the value of y is "; cout << b; getch(); } Output: The value of x is 10 and the value of y is 6

4.1.3 Arithmetic Operators C++ has 5 basic arithmetic operators. Operator Addition Subtraction

Symbol Action + Adds two operands Subtracts the second operand from the first operand Multiplication * Multiplies two operands Division / Divides the first operand by the second operand Modulus % Gives the remainder when the first operand is divided by the second operand

Example x+y x-y x*y x/y x%y

Table 4.1 – Arithmetic operators Operations of addition and subtraction are performed using their respective mathematical operators and for multiplication and division, computing symbols * and / are used.

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Modulo performs a bit different operation. It gives the remainder of a division of two values. ¾ int value= 10 % 3 result in giving 1 as the answer since 1 is the remainder from dividing 10 from 3. 100 modulus 9 equals 1 40 modulus 6 equals 4 ¾ In using arithmetic operators, a suitable data type needs to be chosen in defining variables. e.g., unsigned int difference; unsigned int num1= 7; unsigned int num2= 9; difference = num1- num2; Here you would expect -2 as the answer, but -2 cannot be stored in the unsigned int variable. Just like we have explained in session 2 unsigned variables doesn’t hold negative values. Hence this can lead to unexpected, incorrect outcomes. ¾ int num1= 5 int num2 = 2 int division; division = num1/num2; You would expect an answer as 2.5 but as ‘division’ is defines as an int type variable; it cannot hold a number with a fraction. Here you get the answer as 2, which is incorrect. As a solution ‘division’ can be defined as a floating point variable. Float division; ¾ answer= 3/0; Above statement is incorrect because it is illegal to divide a number by zero. This results in a runtime ‘division-by-zero failure’ which typically causes the programme to terminate.

Activity 4.1 – Working with Arithmetic Operators Write a programme, which ask the user to input 2 integer values. Then your programme should perform addition, subtraction, multiplication, and division on the values the user entered and display the results on the screen.

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4.1.4 Relational Operators C++ provides 6 relational operators for comparing numeric quantities. Operator Equal Greater than

Symbol == >

Less than Greater than or equal to Less than or equal to Not equal

< >= <= !=

Action Is operand 1 equal to operand 2? Is operand 1 greater than operand 2? Is operand 1 less than operand 2? Is operand 1 greater than or equal to operand 2? Is operand 1 less than or equal to operand 2? Is operand 1 not equal to operand 2?

Example x==y x>y x= y x <= y x != y

Table 4.2 – Relational operators ¾ In order to evaluate a comparison between two expressions relational operators are being used. The result of a relational operation is a boolean value that can only be true or false. (4 = = 3) // boolean value is false as 4 is not equal to 3 (8 > 2) // boolean value is true as 8 is greater than 2 (4 != 9) // boolean value is true as 4 not equals to 9. (10 >= 10) // boolean value is true as 10 is eqals to 10. (11 >= 10) // Here this expression also gives the boolean value as true since 11 is greater than 10. (6 < 6) // boolean value is false as 6 is not less than to 6. ¾ ‘Greater than or equal to’ and ‘Less than or equal to’ operators have to be used exactly as shown in the above table. Expressions like => and =< are invalid. ¾ Characters are valid operands since they are represented by numeric values. (e.g., ASCII coding) Hence,‘A’<’F’ is a valid expression. Note: Strings cannot be compared using the comparison operators. C++ provides separate functions to compare strings.

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4.1.5 A demonstration of the use of the Relational operators #include #include void main() { clrscr(); int x,y; cout<<"Enter value1:"; cin>>x; cout<<"Enter value2:"; cin>>y; cout<<"\n"; if(x>y) cout<<"Value1 is larger than value2"; else if (x
4.1.6 Logical Operators Logical operators also evaluate to Boolean value true or false. Operator Symbol Action Logical And && True only if both exp1 and exp2 (AND) are true; false otherwise Logical or (OR) || True only if both exp1 and exp2 or either exp1 or exp2 is true; false otherwise Logical ! False if exp1 is true; true if exp1 negation (NOT) is false Table 4.3 – Logical operators

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Example exp1 && exp2 exp1 || exp2 !exp1

¾ The operator && denotes Boolean logical operation AND. x y x && y true true true true false false false true false false false false ( (7 == 7) && (5 > 7) ) // boolean value is false (true && false) ¾ The operator || denotes Boolean logical operation OR. x y x || y true true true true false true false true true false false false ( (7 == 7) || (5 > 7) ) // boolean value is true (true || false). ¾ The negation operator performs the Boolean operation NOT. !(10= =10) // Boolean value is false because the expression at its right (10 is equal to 10) is true. !(8<=2) // Boolean value is true because the expression at its right (8 is not less than 2) is false.

4.1.7 A demonstration on the use of the Logical operators 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. int eligib, final; 7. 8. 9. 10. 11.

cout<<"Enter your Eligibility marks:"; cin>>eligib; cout<<"Enter final exam marks:"; cin>>final; cout<<"\n";

12. if((eligib>=40) && (final>=40)) 13. cout<<"You have passed the subject"; 14. else 15. cout<<"You have not passed the subject"; 16. getch(); 17. } 42

Output: Enter your Eligibility marks: 55 Enter final exam marks: 40 You have passed the subject In the above programme only if both the eligibility marks and final exam marks are more than 40, it will display the message as passing the subject. Note: If and else statements (line 12 and 14) will be discussed in future sessions.

4.1.8 Increment and Decrement Operators Operator Auto Increment (prefix) Auto Increment (postfix) Auto decrement (prefix) Auto decrement (postfix)

Symbol ++ ++ ---

Action Increment occurs before the variable value is used Increment occurs after the variable value is used decrement occurs before the variable value is used decrement occurs after the variable value is used

Example ++x x++ --x x--

Table 4.4 – Increment and Decrement Operators The increase operator (++) and the decrease operator (--) increase or decrease the value stored in a variable. ¾ In prefix form, the operator is applied first and the outcome is then used. In postfix form, expression is evaluated first and then the operator is applied. x=2; y=++x; // After one execution x=3 and y=3. x=2; y=x++;//after one execution y=2 and x=3 ¾ In increment/decrement operators, the variable can only be incremented or decremented by one value. To increment or decrement a value in a variable by a larger or smaller value, it should be stated as below. x += 3; //this is equal to x=x+3 amount -= 2; //this is equal to amount=amount – 2 Note: increment and decrement operators work only with integer variables

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4.1.9 A demonstration on the use of the decrement operators 1. #include 2. #include 3. int a,b; 4. void main() 5. { 6. clrscr(); 7. //Set a and b both equal to 9 8. a=b=9; 9. // Print them, decrementing each time. 10. cout<<"\n"<
8 7 6

4.1.10 Conditional (Ternary) Operator The conditional operator takes three expressions and returns a value. If the condition is true it returns one value and if the condition is false it returns a different value. condition ? result1 : result2 If condition is true the expression will return result1, if it is not it will return result2. 4= =6 ? 5: 7 // returns 7 as the condition is false (4 is not equal to 6) 8 rel="nofollow">6 ? x:y //returns x as condition is true (8 is greater than 6) 8= =4+4 ? 6:9 //returns 6 as condition is true. (4+4 is real to 8)

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4.2 Precedence of operators In C++ there is an established order for the priority of each operator. This is called the precedence of operators. The precedence is established for all the operators which can appear in C++. From greatest to lowest priority, the priority order is shown in the table given below. Rank 1 2

4 5 6 7 8 9 10 11 12 13 14 15 16

Name scope resolution member selection, subscripting, function calls, postfix increment and decrement sizeof, prefix increment and decrement, complement and not, unary minus and plus, address of and dereference, new, delete, casting member selection for pointer multiply, divide, modulo add, subtract shift inequality relational equality, inequality bitwise AND bitwise exclusive OR bitwise OR logical AND logical OR conditional assignment operators

17 18

throw operator comma

3

Operator :: . -> ()++ -sizeof() ++ -- ^ ! - + & * new[] delete[] () .* ->* */% +<< >> < <= > >= == != & ^ | && || ?: = *= /= %= += -= <<= >>= &= |= ^= throw ,

Table 4.5 – Precedence of operators Operator precedence is defined in order to overcome some of the problems in performing calculations. For example, sometimes it is difficult to decide which operation to perform first. Ex. a= (3+5)*7. According to the above table () has a higher precedence than multiplication. Hence expression inside the () should be performed first (3+5=8) and then the multiplication. The answer is 56.

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Activity 4.2 – The use of Conditional (Ternary) Operator

Write a programme, which asks the user to input 2 integer values. Then your programme should identify the largest value (using the conditional operator) out of the two integers and display it on the screen.

Summary ¾ An operator is a symbol, which performs a certain action in a programme. Mainly there are 5 categories of operators namely, assignment operator, arithmetic operator, logical operator, relational operator, increment and decrement operator. ¾ The assignment operator (=) assigns a certain value to a variable. ¾ There are 5 basic arithmetic operators. They are addition (+), subtraction (-), multiplication (*), division (/) and modulus (%). ¾ Relational operators are used for comparing numeric quantities. There are 6 relational operators, which are equal, greater than, less than, greater than or equal to, less than or equal to and not equal. ¾ Logical operators in C++ evaluate to Boolean value true or false. Three basic logical operators are logical AND (&&), Logical OR (||), Logical negation (!) ¾ The increase operator (++) and the decrease operator (--) increase or reduce the value stored in a variable. ¾ The conditional operator takes three expressions and returns a value. condition? result1: result2 ¾ In C++ there is an established order for the priority of each operator. This is called the precedence of operators.

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Session 4 - Answers Activity 4.1- Answer #include #include

void main() { clrscr(); float val1,val2,tot,sub,mul,div; //take the user input cout<<"Enter an integer:"; cin>>val1; cout<<"Enter another integer "; cin>>val2; //Calculate values tot=val1+val2; sub=val1-val2; mul=val1*val2; div=val1/val2; //Displaying the output cout<<"\nAddition:"<
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Activity 4.2 - Answer #include #include void main() { clrscr(); int x,y; //take the user input cout<<"Enter value1:"; cin>>x; cout<<"Enter value2:"; cin>>y; //finding the largest value int answer=(x>y ? x:y); //displaying the output cout<<"\n"<
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Session 5 C++ Control Structures Contents Objectives Introduction 5.1 Conditional Statements 5.1.1 The if statement 5.1.2 The else statement 5.1.3 The else if statement 5.1.4 A demonstration on use of if and else statements. 5.2 Iteration Structures (loops) 5.2.1 The while loop 5.2.2 Demonstration on use of while loop 5.2.3 The do-while statement 5.2.4 A demonstration on use of do-while statement 5.2.5 The for loop 5.2.6 A demonstration on use of for loop 5.2.7 Multiple initializations and increments 5.2.8 A demonstration on the use of multiple initializations and increments 5.3 Nested Control Statement 5.3.1 A Demonstration on use of nested loops 5.3.2 A Demonstration on the use of loops and conditional statments Summary

Objectives After reading this lesson you should be able to: ¾ Branch your programming code based on conditions ¾ Understand what loops are and how they are used ¾ Build various types of loops.

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Introduction Usually a programme is not limited to a linear sequence of instructions. During execution, it may branch off to different parts of a programme, repeat code or take decisions. ‘Control structures’ assist in serving these kinds of special purposes. This session introduces various forms of C++ control structures for composing programmes. These conditional statements and iteration structures are used almost in every programme. In addition they are nested in order to produce more complex and powerful programmes.

5. 1 Conditional Statements The conditional statements are used to make an execution choice in a programme based on a given condition. The if and else statements are the main conditional statements in C++.

5.1.1 The if statement The ‘if’ statement enables to check for a given condition and it also helps to branch to different parts of the programme depending on the result. The general format of the if statement is: if (condition) Statement; The programme checks for the condition and when the condition is true, the statement is executed and when the condition is false, the statement is ignored (not executed) and the program continues. Example 1:

if (balance rel="nofollow">0) interest = balance * credit rate;

The if statement can control the execution of multiple statements by the use of a compound statement, or block. (A block is a group of two or more statements enclosed in curly braces) Any number of statements can be included inside this block. if (condition){ Statement 1; Statement 2; } Example 2:

if (balance>0) { Interest = balance * credit_rate; balance = balance + interest; }

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5.1.2 The else statement Additional operations can be specified using the keyword ‘else’. if (condition) { Statement 1; } else Statement 2; When the condition in the if statement is evaluated as true, statement1 is executed. Otherwise the else statement is evaluated and the statement 2 is executed. The else statement can also have multiple statements to execute. We use a block for this purpose. else { Statement 1; Statement 2; }

5.1.3 The else if statement In C++ programming, a nested if statements can be used. if ( ch>=’0’ && ch<=’9’ ) type = digit; else{ if ( ch>= ‘A’ && ch<= ‘Z’ ) type = capital_letter; else { if ( ch>= ‘a’ && ch<= ‘z’ ) type = simple_letter; else type = special; } } Compound statements given above are complex to understand. Hence, the else if statements are used. if ( ch>=’0’ && ch<=’9’ ) type=digit; else if ( ch>= ‘A’ && ch<= ‘Z’ ) type = capital_letter; else if ( ch>= ‘a’ && ch<= ‘z’ ) type = simple_letter; else type = special;

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5.1.4 A demonstration of the use of if and else statements. #include #include int x, y; void main() { clrscr(); // Input the two integer values cout<<"Enter an integer value1: "; cin>>x; cout<<"Enter another integer value2: "; cin>>y; // Test values and print result if (x == y) cout<<"\nValue1 is equal to value2\n"; else if (x > y) cout<<"\nValue1 is greater than value2\n"; else cout<<"\nValue1 is smaller than value2\n"; getch(); } Output: Enter an integer value1: 35 Enter another integer value2: 35 Value1 is equal to value2

Activity 5.1 – Examining the ‘else if statement’ Write a programme which inputs a person’s height (in meters) and weight (in kilograms) and the output as one of the messages: underweight, normal or overweight. Underweight: BMI<18.5 Normal: 18.5<= BMI <=25 Overweight BMI>25 Use the formula given below to calculate a persons BMI value: BMI (Body Mass Index): (weight) kg/ (height*height)m

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5.2 Iteration Structures (loops) Iteration structures or loops are used to repeat one or more steps in a programme depending on conditions. In C++ there are three basic iterations structures. They are the while loop, do-while loop and the for loop. The diagram given below shows the iteration structure of a loop in general.

Figure 5. 1: The operation of C++ loops

5.2.1 The while loop The while loop first check the given condition and when the condition is true, it executes the statement or statements and exit the loop when the condition becomes false. The general form of while statement is: while (condition) Statement; The while loop consists of either a single statement or multiple statements. When there is more than one statement it has to be included inside curly braces which we call a block. while (condition) { Statement1, Statement2; }

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5.2.2 Demonstration of the use of while loop 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. int x = 0; 7. while (x<3) { 8. cout<<"Before increment:"<<x<<"\t"; 9. x++; 10. cout<<"After Increment:"<<x<<"\n"; 11. } 12. getch(); 13. } Output: Before increment: 0 Before increment: 1 Before increment: 2

After Increment: 1 After Increment: 2 After Increment: 3

The table given below illustrates the operations of a while loop. Iteration First Second Third Forth

Value of X (Before) 0 1 2 3

Check for x<3 0<3-condition true 1<3-condition true 2<3-condition true 3<3-condiiton false

Increment 0++ 1++ 2++

Value of x (After)

1 2 3 Exit while loop

Table 5. 1 - The operation of a while loop. In line 6 of the example given above, x is assigned to 0. In the first iteration the condition (0<3) is initially checked (line 7). As the condition becomes true it starts executing the statements inside the block. It prints the value 0 (line 8) and increment the value of x by 1(line 9). After the increment x becomes 1 and the printed output in line 10 verifies it. (Refer the programme output-after increment:1). The while loop checks for the condition again as the value of x is now 1. Hence it checks whether 1<3. Then it executes the statements inside the block and prints the values and

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increment x again. This loop continues until the condition being false when x becomes 3 and 3<3 statements is false. Then the programme exit from the loop Every while loop has to end at some point. Therefore, there should be a method which makes the while statement false at a given point (when x becomes 3), otherwise the loop will continue looping forever.

5.2.3 The do-while statement The do-while loop and the while loop is similar in nature except for a minor difference. In the while loop it is possible that the body of it will never be executed, if the condition becomes false, but using the do-while loop the body of the loop will be executed at least one time. Hence in do-while loops the body is executed first and then the condition is checked. The general format of do-while is: do statement while (condition); Do while loop also can have a single statement or multiple statements to execute.

5.2.4 A demonstration of the use of do-while statement 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. unsigned short number; 7. do { 8. cout << "Enter number (0 to 65535): "; 9. cin >> number; 10. cout << "You entered: " << number << "\n\n"; 11. } while ( number!=100 ); 12. getch(); 13. } Output: Enter number (0 to 65535): 3344 You entered: 3344 Enter number (0 to 65535): 100 You entered: 100 55

In the above programme, every time the message in line 8 will be displayed for the user to enter a value and then it will be displayed as ‘You entered ’(line 10), followed by the number the user entered. This continues until the user enters the value 100. Then it will also be displayed as ‘You entered: 100’ and only after displaying the message it will check for the condition whether 100!=100. Here as the condition becomes false it will exit the loop and the programme will be terminated.

5.2.5 The for loop This is also similar to the while loop and its main function is also to repeat statements, but the for loop is powerful and flexible to use. In addition, it provides a specific location for the initialization, condition and for the increase or decrease operator. The general format of the for loop is: for (initialization; condition; increase/decrease) statement; The most common use of for loops is for situations where a variable is incremented or decremented with every iteration of the loop.

5.2.6 A demonstration of the use of for loop 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. int total = 0; 7. for (int x=0;x<=5;++x){ 8. total = total + x; 9. cout<<"\nTotal is: "<
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The for loop also operates in a similar way to the while loop. In line 7, the loop first initialize x to 0. Then it checks for the condition and if the condition is true it performs the operations inside the body. (Lines 8 & 9). Then it comes to line 7 again and increment the value of x by 1 and then checks the condition (whether 1<=5) and this continues until the condition becomes false.

5.2.7 Multiple initializations and increments In the above example, only a single variable is initialized and incremented in a for loop, but it is possible to initialized multiple variables and they can be incremented or decremented accordingly.

5.2.8 A demonstration of the use of multiple initializations and increments #include #include void main() { clrscr(); for (int a=0, b=3; a<3; a++, b--) { cout<<"a="<
b=3 b=2 b=1

In the above example ‘a’ is incremented and ‘b’ is decremented at the same time and when variable ‘a’ becomes 3 the condition becomes false and the programme exits from the for loop.

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5.3 Nested Control Structures Control structures can be nested to produce more complex programmes. Here the Loops can be nested, which means one loop can appear inside another loop. The conditional statement can also appear inside the loops.

5.3.1 A Demonstration of the use of nested loops The programme given below, produce the product of set {1, 2, 3} #include #include void main() { clrscr(); for (int x=1;x<=3;++x){ for(int y=1;y<=3;++y) cout<<"("<<x<<","<
Output: (1,1) (1,2) (1,3) (2,1) (2,2) (2,3) (3,1) (3,2) (3,3)

5.3.2 A Demonstration of the use of loops and conditional statements 1. #include 2. #include 3. #include<stdlib.h> 4. void main() 5. { 6. clrscr(); 7. 8. 9. 10. 11. 12. 13. 14. 15.

int code=1122; int user; cout<<"You are given only 3 attempts to enter the 4 digit code.\n"; for (int a=0;a<3;a++){ cout<<"Enter the code:"; cin>>user; if (code==user){ cout<<"Congratulations….Code is correct!\n"; getch(); 58

16. 17. 18. 19. 20. 21.

exit(0); } else { cout<<"Code is incorrect!\n\n"; } }

22. getch(); 23. } Output: You are given only 3 attempts to enter the correct code. Enter the code: 1178 Code is incorrect! Enter the code: 5678 Code is incorrect! Enter the code: 1122 Congratulations….Code is correct!

The above programme is similar to a typical password checking programme. The user is given 3 attempts to enter the correct code and this is done by the use of a for loop. When the user is unable to enter the correct code in 3 attempts, the programme terminates as it exits from the for loop. If the user enters the correct code in any of the given attempts, it will display the message ‘Congratulations….Code is correct!’ in line 14. Then it exits the programme because of the ‘exit (0)’ statement in line 16, which is defined in the <stdlib.h> library.(line 3)

Activity 5.2 Write a programme, which produces the following output. ****** ****** ****** ****** ****** Hint: Use nested loops.

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Summary ¾ Conditional statements are used to make an execution choice in a programme based on a given conditions. There are two main control structures: if and else. ¾ The else if statements are used to reduce the complexity of compound statements. ¾ The iteration structures help to execute a set of statements repeatedly. There are three main iteration structures, while loop, do-while loop and the for loop. ¾ All the iteration structures first perform the operations in the initialization, and then evaluate the condition. If the condition is true, it executes the action statement and the loop. When the condition becomes false it exits the loop. ¾ There are three iteration structures in C++ and they are slightly different in nature because of their operation and use. ¾ The while loop first checks the given condition, and when the condition is true, it executes the statement or statements inside the block. ¾ The do while loop first execute the statements and then check whether the given condition is true. Hence in do-while loops the statements are being evaluated at least once. ¾ For loop is more flexible to use than the other iteration structures. ¾ When a loop appears inside another loop we call them nested control statements and conditional statements can also be included inside loops.

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Session 5 - Answers

Activity 5.1 - Answer #include #include void main() { clrscr(); //defining variables float height,weight,bmi; //taking user input (weight and height) cout<<"Enter your height(in meters):"; cin>>height; cout<<"Enter your weight(in kilograms):"; cin>>weight; //Calculating BMI value bmi=weight/(height*height); //when BMI value is less than 18.5 if (bmi<18.5) cout<<"You are underweight!"; //when BMI value is between 18.5 and 25 else if(bmi<=25) cout<<"You are Normal!"; //When BMI value is more than 25 else cout<<"You are Overweight!"; getch(); } Output: Enter your height (in meters): 1.8 Enter your weight (in kilograms): 60 You are Normal!

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Activity 5.2- Answer #include #include void main() { clrscr(); for (int x=1;x<=5;x++){ for(int y=6;y>0;y--){ cout<<"*"; } cout<<"\n"; } getch(); } Output: ****** ****** ****** ****** ******

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Session 6 More Control Structures Contents Objectives Introduction 6.1 Jump Statements 6.1.1 The Break statement 6.1.2 A demonstration on the use of break statement 6.1.3 The continue statement 6.1.4 A demonstration on the use of continue statement 6.1.5 The goto statement 6.1.6 A demonstration on the use of goto statement 6.2 The switch statement 6.2.1 A demonstration on the advantage of the break statement inside a switch 6.2.2 A demonstration on the use of goto statement Summary

Objectives After reading this lesson you should be able to: ¾ Understand what jumping statements are and how they are used. ¾ Branch your programming code in to different parts of the programme using these statements. ¾ Build various types of switches depending on the programme need.

Introduction The previous session introduced the conditional statements used in C++, which help in taking decisions, and also the iteration structures which assist in repeating a written code. This session focuses on the jumping statements in C++ which is another form of control structures that are used in writing programmes. Most of these jumping statements need to be included inside a while, do-while or a for loop. In general a programme has a sequential flow but using these statements it is possible to change the flow of the programme in order to serve a specific purpose that we require. This session also introduces the switch statement which is similar to the else-if statement we learned in the previous session. 63

6.1 Jump Statements These statements assist in changing the direction of the execution of programmes by jumping from one part of the programme to another part. There are three main jump statements in C++. They are the break statement, the continue statement and the goto statement.

6.1.1 The Break statement A break statement should be included inside a loop (whole, do-while, for) or inside a switch. This statement can be used to end an infinite loop, or to force it to end before its natural end. Including this in a loop or in a switch makes the execution jumps to the closing braces of the loop or the switch.

6.1.2 A demonstration of the use of break statement 1. #include 2. #include 3. void main () 4. { 5. clrscr();

6. 7. 8. 9. 10. 11. 12.

//A counter which counts from 10 to 0 for (int counter=10; counter>0; counter--){ cout << counter<< "\n"; if (counter==5) { cout << "Counting END!\n"; break; } }

13. getch(); 14. } Output: 10 9 8 7 6 5 Counting END! 64

In the above programme the counter starts from 10 (line 6) and in each iteration decrease its value by 1. In every iteration when it comes inside the for loop, it checks whether the counter value is equal to 5 and when it becomes true, it prints the message in line 9 and exits the loop. Note: Even though the for loop is initialized to iterate 10 times (10 to 0), the programme exits the loop because of the break statement in line 10. In the previous session in the demonstration 5.3.2 the exit function is used to exit from the programme when the user enters the correct code. This same action can be achieved with the use of the ‘break’ statement as shown below. . if (code==user){ cout<<"Congratulations….Code is correct!\n"; break; }

Activity 6.1 – Analysing the behavior of the ‘break’ statement Write the above prgramme (6.1.2) using your text editor, remove the break statement, compile and run the programme. What is the output?

6.1.3 The continue statement The continue statement should also be included inside a loop. This statement terminates the current iteration of a loop and instead jumps to the next iteration. It applies to the loop immediately enclosing the continue statement, and not to the outer loops. Example below shows a part of a programme. while (category) { for (int a=0;a>num; if(num<0) continue; // statements ……. } //statements } In the above example the continue statement applies to the for loop. (not to the while loop)

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6.1.4 A demonstration of the use of continue statement 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. int x=0; 7. do 8. { 9. 10. 11. 12. 13. 14.

x++; cout<<"Value of x is "<<x<<"\n"; continue; cout<<"After the continue statement"; } while (x < 3);

cout<<"After the do loop!";

15. getch(); 16. } Output: Value of x is 1 Value of x is 2 Value of x is 3 After the do loop! In the above programme, x in initialized to 0. When the programme is executing and when it comes inside the do-while loop it first increments the value of x by 1. Then it prints the massage ‘Value of x is 1’ and because of the continue statement in line 11, it skips printing the massage ‘after the continue statement’. Next, the programme comes to the loop condition in line 13 and check for the condition whether 1<3. As the condition becomes true it starts its second iteration. The loop continues until x becomes 3 and the condition in line 13 becomes false when 3<3 is false. Then, it exits the loop and print the message ‘After the do loop!’ and the programme ends. Notice that inside the do-while loop, the line 12 will never be executed because of the continue statement in line 11 terminated the current iteration of the do-while loop. Note: In compiling the above programme a warning message will be displayed as ’Unreachable code’ since line 12 will not be executed.

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6.1.5 The goto statement The goto statement allows jumping from one point of the programme to another point. A goto statement consists of a label, some statements, and a jump. It has a general form: goto label: The label is the identifier, which marks the jump destination of goto statement. This statement can causes a jump to any location in the source code, backward or forward but it should be used with caution since its execution causes an unconditional jump.

6.1.6 A demonstration of the use of goto statement 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. 7. 8. 9.

int num,square; start: cout<<"Enter an integer less than 10:"; cin>>num;

10. 11. 12. 13. 14. 15. 16. 17.

if (num<10){ square=num*num; cout<<"Square of "<
18. getch(); 19. } Output: Enter an integer less than 10: 88 Illegal number! Enter an integer less than 10: 9 Square of 9 is 81

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In the above programme the user is asked to input only a number less than 10 and calculates its square. If the user enters a value which is more than 10 it execute the else statement (line 14), prints the massage in line 15 and execute the goto statement in line 16, which makes the programme jump back to line 7. Then it begins executing the programme from line 8. Note: In the above programme the use of the goto statement prevents the programme from terminating until the user enters a value which is less than 10.

6.2 The switch statement Switch statements are also called ‘case statements’ which provides a way of choosing between a set of alternatives based on a value of an expression. It also helps to control the flow of program execution. The general form of a switch statement is. switch (expression) { case constant1: group of statements 1; break; case constant2: group of statements 2; break; default: default group of statements; break; } Each block begins with a line containing the case keyword followed by an expression. The expression is evaluated and the outcome is compared to each of the constants. If the expression outcome matches the constant, the execution jumps to those statements which is under the particular constant and continues to execute the ‘group of statements’. When the programme reaches the break statement under that particular constant, it exits from the switch statement. It is necessary to include the break statement after the group of statements in every case. If the break statement wasn’t included the program will continue executing the rest of statements until it reaches either a break instruction or the end of the switch statement. We can take advantage of this feature in writing programmes.

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6.2.1 A demonstration of the advantage of the break statement inside a switch 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. int day; 7. cout<<"Enter a number between 1 and 7:"; 8. cin>>day; 9. 10. 11. 12. 13. 14. 15. 16.

switch (day) { case 1: case 2: case 3: case 4: case 5: cout << "Week Day!"; break;

17. 18. 19. 20.

case 6: case 7: cout << "Week end!"; break;

21. 22. 23.

default: cout << "Illegal day number!"; }

24. getch(); 25. } Output: Enter a number between 1 and 7: 6 Week day!

In the above programme, for any of the constants 1, 2, 3, 4, 5 it prints the output as ‘Week Day’ and exit the switch because of the break statement. For both constants 6 and 7 it prints Weekend. If the user enters any other value it executes the default statement and prints the message in line 22 as ‘Illegal day number!’.

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In C++ , a case can be left as blank but there is no point in having a case blank unless there is a useful action to be performed. For example, in the above programme case 1,2,3,4 and 6 are blank because the same operation is required to perform for each of the cases. Here the programmer doesn’t need to specify the group of statements under each constant saving the programmers effort and time. In switch statements, if the expression doesn’t match any of the constants, the programme branches to the optional default statement. If there is no default and there is no matching value, execution falls through the switch statement and the statement ends.

6.2.2 A demonstration of the use of switch statement #include #include void main() { clrscr(); int day; cout<<"Enter a number between 1 and 7:"; cin>>day; switch (day) { case 1 : cout << "Sunday"; break; case 2 : cout << "Monday"; break; case 3 : cout << "Tuesday"; break; case 4 : cout << "Wednesday"; break; case 5 : cout << "Thursday"; break; case 6 : cout << "Friday"; break; case 7 : cout << "Saturday"; break; default : cout << "Illegal day number!"; break; } getch(); }

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Output: Enter a number between 1 and 7: 6 Friday Here the switch statement is similar to an ‘else if’ statement (refer session 5), hence the above programme can be written as given below. if (day==1) cout<<”Sunday”; else if (day==2) cout<<”Monday”: else if (day==3) cout<<”Tuesday”; else if (day==4) cout<<” Wednesday”; else if (day==5) cout<<” Thursday”; else if (day==6) cout<<” Friday”; else if (day==7) cout<<” Saturday”; else cout<<” Illegal day number!”; However the ‘switch’ statement is flexible to use than the ‘else if’ statements. Hence it is advisable to use else-if statements only on the circumstances where the switch statements cannot be used. For example when the conditions involve are not equality expressions etc

Activity 6.2 – Writing a programme using the ‘switch’ statement Write a programme which asks the user to input a grade (A,B,C or D). Display the following messages depending on the input. A or a=Your average must be between 90 – 100 B or b=Your average must be between 80 – 89 C or c=Your average must be between 70 – 79 D or d=Your average must be between 60 – 69 If the user enters any other grade the programme should display: Your average must be below 60. Note: If the user enters even a lower case letter (a,b,c,d), the programme should display the same messages.

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Summary ¾ Jumping statements assist in changing the direction of the execution of pogrammes by jumping from one part of the programme to another part. Break, continue and goto statements are mainly used in this purpose. ¾ A break statement should be included inside a loop (whole, do-while, for) or inside a switch. This statement is used to exit the loop before the exit conditions are met. ¾ The continue statement helps to jump back to the top of the loop, before the entire set of statements in the loop is executed. This should be also included inside a loop. ¾ The goto statement is used to jump from one point of the programme to another point. These statements should be used with care and use it only when it is essential. ¾ Switch statements or case statements are one of the most frequently used programming techniques in C++ in choosing between a set of alternatives based on a value of an expression. This is also an alternative to deeply-nested if/else statements.

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Session 6 - Answers Activity 6.1 Answer Output:

10 9 8 7 6 5 Counting END! 4 3 2 1

Activity 6.2- Answer #include #include void main() { clrscr(); char grade; cout << "Enter your grade: "; cin >> grade; switch (grade) { case 'a': case 'A': cout << "Your average must be between 90 - 100"; break; case 'b': case 'B': cout << "Your average must be between 80 - 89"; break; case 'c':

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case 'C': cout << "Your average must be between 70 - 79"; break; case 'd': case 'D': cout << "Your average must be between 60 - 69"; break; default: cout << "Your average must be below 60"; } getch(); } Output: Enter your grade: B Your average must be between 80 - 89

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Session 7 Basics of Functions Contents Objectives Introduction 7.1 What is a function? 7.2 Declaring and defining a function 7.2.1 A demonstration of the use of functions 7.2.2 Declaring a function 7.2.3 Defining a function 7.2.4 The return statement 7.2.5 Calling a Function 7.3 The execution of a function 7.4 Assigning default values to parameters 7.5 Advantages in using functions Summary

Objectives After reading this lesson you should be able to: ¾ Understand what is a function is and what its components are. ¾ Declare and define functions. ¾ Pass parameters into functions. ¾ Return a value from a function.

Introduction Functions are one of the most important aspects of program design. Using functions a programme can be properly structured. A function is a piece code that performs a specific task. Some functions are supplied as part of the compiler package but this session mainly focuses on the functions that the user can create. In writing a function, the first step is to know what tasks the function needs to perform. In addition, a function has a specific format and it needs to be followed in creating functions. 75

7.1 What is a function? A function can be called as a sub programme which manipulates data and performs a specific task in a programme. Every program has at least a single function. For example every programme contains the function called main(). (main() function was discussed in session1) There are two types of functions: 1. User-defined: The programmer can define his or her own functions. 2. Built-in: These functions are part of the compiler package, which are supplied by the manufacturer and can be used in writing programmes. (Ex main (), getch(), clrscr() etc) The general format of a function is: return_data_type function_name ( parameter1, parameter2, ...) { statements; } ¾ The ‘return_data_type’ is the data type that is returned by the function. ¾ The ‘function_name’ is the name or the unique identifier of the function. ¾ The ‘parameters’ consists of a data type followed by the name of the parameter, (example: int x) A function can have zero or any number of parameters separated by commas. ¾ The ‘statements’ are called the body of the function. It is a block of statements surrounded by braces { }.

7.2 Declaring and defining a function In creating functions they need to be declared and defined. These concepts will be covered using the example programme given below.

7.2.1 A demonstration of the use of functions 1. #include 2. #include 3. int addition (int x, int y); 4. void main () 5. { 6. clrscr();

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7. int answer; 8. answer = addition (4,5); 9. cout << "The result is " << answer; 10. getch(); 11. } 12. int addition (int x, int y) 13. { 14. int total; 15. total=x+y; 16. return total; 17. } Output: The result is 9

7.2.2 Declaring a function The declaration includes the function return type, function name, and parameter list. This is also called the prototype of the function. There are three ways to declare a function: 1. Write the prototype into a file, and then use the #include directive to include the function in the program. Example 7.1: In the programme given above the functions like clrscr() (line 6), getch() (line 10) are included in the file and we include it in our programme using ‘#include’ (line 2). 2. Write the prototype at the beginning of the file (before the main method) in which the function is used. Example 7.2: In the above programme the prototype of the function is given in line 3: int addition (int x, int y); 3. Define the function before it is called by any other function. Here the definition of the function acts as its own declaration. Example 7.3: The above programme can be written without a prototype #include #include

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int addition (int x, int y) { //statements } void main() { //statements } In the above programme the function can be included before the main () function. In a situation like this there’s no need of a prototype, but it is advisable to use a prototype in programmes for many reasons. Some of the reasons are given below. 1. If a prototype is not used, the functions need to be included in a particular order making it difficult to maintain and change the programme in the long run. 2. Sometimes a function may call another function and that function in return can call the first function (function x calls function y and function y can call function x again) In these complex situations it is hard to decide which function should be included first. Hence the function prototype needs to be declared.

7.2.3 Defining a function The definition of a function includes the header and its body. The header is the ‘function return type’, ‘function name’ and ‘parameter list’. Example 7.4: int addition (int x, int y) (line 12) The function return can be a null value, which means there can be functions, which do not return any value. These functions are declared using the keyword ‘void’. Example 7.5: The main function that is been used so far is a function, which does not return any value. These functions are mostly used when we want to print a message on the screen. Here no value needs to be returned in order to print a message. In addition, the parameter list can be left blank if the function needs no parameters. The example given below is also a user defined function which prints the message “This is a function!” Example 7.6:

void message () { cout << "This is a function!"; }

The void keyword can also be used in the function's parameter list to explicitly specify that the function does not take any actual parameters when it is called. For example, function message could have been declared as:

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void message (void) { cout << "This is a function!"; } Even though some functions don’t return any value, they can contain a parameter or a list of parameters. Example 7.8: void PrintMessage(int messageSelect) { if (messageSelect == 0) cout << "Start of Programme.\n"; if (messageSelect == 1) cout << "End of programme.\n"; } The body of a function includes the statements (computation steps) inside the curly braces {} which contains the instructions on how to perform a specific task. Example 7.9: In the programme given in 6.2.1, line 13 to 17 is the body of the function. { int total; total=x+y; return total; }

7.2.4 The return statement In the example given above, in line 16, the return keyword has been used followed by an expression. This is called the ‘return statement’. It should be declared inside the function body. The return statement has a general format. return expression; Expression is the value returned by the function. The type of this value should be same as the return type of the function. Example 7.10: In the programme given above the type of the function is an integer. (int addition) hence the return value ‘total’ should also be an integer value. For a function who’s return type is void, expression should also be 0 or empty. The main function can also be written as below. int main(void){ cout<<”Open University”; return 0;

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Note: In declaring the prototype of a function, it is not necessary to include the names of the parameters. The type of the parameter list is also sufficient. Example: int calculate (int ,int);

7.2.5 Calling a Function Using a function involves calling the function. A function call consists of function name followed by the call operator brackets’ ()’. Inside the call operator brackets a function arguments appears. The value that is returned by the return statement is the point where the call occurs. Example 7.11: calculate (5, 6); Here the number of arguments should match the number of function parameters. Example 7.12: int calculate function has only two parameters which is int x and int y. In the calling function inside the call operator brackets’ ()’ there should be only two arguments which are 5 and 6. Not only the parameters but also the type of the parameter should match the function parameters. Example 7.13: Both function parameters x and y are of type int. Hence the argument values also should be of type int. (5, 6). It cannot be a floating point or other type of a value.

7.3 The execution of a function Regardless of whether a function is declared before the main function, or a function prototype is declared before the main function, the execution of all C++ programmes start from the main function. The general executions of functions are given below. main (){ Function 1 Function2 Statements; ------------Statement; ------------Function1; Function3; Statement1; return ------------------------Function2; return Statement2; Function4; Statement4; }

Function 4 ------------------------return Figure 7.1-Execution of functions 80

Function 3 ------------------------return

Consider the example programme in 7.2.1. First it declares the variable ‘answer’ of type int. Then it branches to the prototype of the function called ‘addition’ in line 3. int addition (int x, int y); When the ‘first' time the function is identified by the program, the above function prototype tells the compiler that the program passes the value of two integers to the function and that the ‘return value’ must be assigned to an integer variable. Then the programme execution passes to the function definition. The arguments are evaluated and their resulting values are assigned to the corresponding parameters. (Here 4 and 5 are passed to int x and y respectively) The body of the function is then executed. (add x and y and store 9 in the variable ‘total’). Finally if there is a value to be returned, it is passed to the caller. (Finally 9 is returned to the variable answer) answer = addition ( 4, 5 ) 9 4

5

int addition ( int x, int y ) After the last statement of the function has been processed (the return statement), the execution resumes on the next line after the call to the function and print the answer. (return to line 9, cout << "The result is " << answer;)

Activity 7.1 – Creating a simple function Write a programme which inputs an integer value between 1 and 10 and output its factorial. Use the formula given below: Factorial(0)=1; Factorial(n)=n*factorial(n-1) Note: When the user enters a value out of the given range it should display an error message and the programme should again ask the user to input a valid integer.

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7.4 Assigning default values to parameters In the beginning of this session we mentioned that the number of arguments in a function call should match the number of function parameters in the given function. Example 7. 14: average (20,1,6)

int average (int a, int b, int c) A programmer can break the above rule by defining default parameter values in the function declaration using the assignment operator, default values can be assigned to the function parameters. Any or all of the function's parameters can be assigned default values. Example 7.15: int add (int x, int y=5, int z=8) When sufficient number of arguments are not supplied for the function, the default parameter values are being used but if a value is specified, this default value is ignored and the passed value is used instead. Note: If any of the parameters do not have a default value, no previous parameters may have a default value. Example 7.16: int add (int x, int y, int z) A default value to x can be assigned only after assigning default values to both y and z. A default value to y can be assigned only after assigning a default value to z.

7.4.1 A demonstration on the use of default parameters 1. #include 2. #include 3. //function prototype 4. int average (int a, int b=2, int c=10); 5. void main () 6. { 7. clrscr(); 8. 9. 10. 11.

//function call and result display cout<< "First average: "<
12. getch(); 13. }

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14. 15. 16. 17. 18. 19. 20.

//function declaration int average (int a, int b, int c) { int result; result=(a+b+c)/3; return result; }

Output: First average: 8 Second average: 9 Third average: 5 In the example given above, in line 4, for b and c default parameters have been assigned. In the first function call (line 9), since 12 is passed as argument to the function, ‘a’ is assigned to the value 12. Since there are no values passed for b and c, it takes the default values which is b=2 and c=10. Then in the first average calculation the result becomes 8. (line 18 -12+2+10/3=8). In the second function call, since all the values have been passed as an argument the compiler ignores the default values and the answer becomes 9. (20+1+6/3 =9). In the third function call, values 1 and 4 are assigned to ‘a’ and b respectively and the default value of 10 is assigned to c. Here also the default value of b is ignored since a value has been passed by the function call.

Activity 7.2 – The use of default parameters Write a function which calculates a volume of a cube. Assign default parameters only to width and length. Call the function 3 times inside the main method. 1. Pass only one argument (both default parameters will be called) 2. Pass two arguments (only one default parameter will be called) 3. Pass all three arguments Write a separate function which prints the message “Volume of the cube”. The output of the programme should appear as given below. Example output: Volume of the cube: 300 Volume of the cube: 3744 Volume of the cube: 1190

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7.5 Advantages in using functions ¾ Enable reuse of code across multiple programs ¾ Reduce the duplication of code in a program (Example: by replicating useful functionality, such as mathematical functions) ¾ decomposing complex problems into simpler pieces maintainability and ease of extension of the programme).

(this

improves

¾ Improve readability of a program. ¾ Hiding part of the program (Information hiding)

Summary ¾ A function can be called as a sub programme which manipulates data and performs a specific task in a programme. ¾ There are two types of functions. They are User-defined functions and build in functions. ¾ There is a general format for a function. This includes TTTTTTTTTTTTTTTTTfunction name, return data type, parameters and a set of statements which is the body of a function. Some functions don’t contain any parameters and every function doesn’t return a value. ¾ In creating functions they need to be declared and defined. The definition of a function includes the header and its body. ¾ There are three ways to declare a function. They are, writing the prototype at the beginning the file, defining the function before it is called by any other function and using the use the #include directive ¾ Function call consists of function name followed by the call operator brackets’ ()’. ¾ The execution of every C++ programme start from the main function. ¾ The programmer can define default parameter values in the function declaration. ¾ There are many advantages in using functions.

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Session 7 - Answers Activity 7.1 - Answer #include #include void main() { clrscr(); // Function prototype int factorial(int value); int number, result; start: cout << "Enter an Integer number between 1 and 10:"; cin >> number; if(number>0 && number<=10) { // Function call and assignment of return value to result result = factorial(number); //Output result cout << "Factorial of "<
} return fact; // This value is returned to caller } Output:

Enter an Integer number between 1 and 10: 6 Factorial of 6 is 720

Activity 7.2- Answer #include #include //function prototypes int volume(int height, int width=5, int length=12); void msg(); void main() { clrscr(); //calling functions msg(); cout<
Session 8 Arrays Contents Objectives Introduction 8.1 What is an array? 8.1.1 Declaring Arrays 8.1.2 Array elements 8.1.3 A demonstration of the use of an integer array 8.1.4 Initializing Arrays 8.2 Multidimensional Arrays 8.2.1. Declaring a two dimensional array 8.2.2 Initializing Multidimensional Arrays 8.2.3 A demonstration of the use of a two dimensional array 8.3 Arrays as parameters to functions 8.3.1 A demonstration of passing an array as a parameter to a function Summary

Objectives After reading this lesson you should be able to: ¾ Understand what arrays are and the correct use of them ¾ Declare and initialize arrays ¾ Work with two dimensional arrays ¾ Pass arrays as parameters into a function

Introduction In the previous sessions we understood that it is essential to declare variables in order to store data. Hence separate variables were created for each data item that needs to be used in programmes. In real world situations it is essential to store not only a couple of data items but hundreds and thousands of data items in a single programme. If we try to declare separate variables for each data item, writing programmes will be a time consuming and tiresome activity. In circumstances like this we cannot merely adopt the approaches we have already learnt.

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This session introduces a method that is used almost in all the programming languages, to overcome the above mentioned problems. If large number of data items needed to be stored, they can be grouped together, using ‘arrays’. In an array any number of data items can be stored.

8.1 What is an array? An array is a set of elements, each of which holds the same type of data. These data elements are stored continuously in the memory.

8.1.1 Declaring Arrays Arrays must be declared before it is used. In declaring arrays two things needed to be taken into consideration. That is: ¾ The type of data items that are required –In a single array all the elements consists of the same data type so the type needs to be specified. ¾ The number of data items required – arrays have a fixed size after declaring it. Hence an array size needs to be specified in advance. The general format of declaring an array is: data type, array name [number of array elements]; In declaring arrays, an array type needs to be declared first (int, char, float etc) followed by the name of the array. In addition, inside square brackets, the exact number of elements needs to be specified. Example 8.1: int marks [5]; The above array declares integer type array named, ‘marks’ which allows storing 5 integer values. In each time an array is declared the memory is separately allocated for each element. Example: 8.2: In the above programme since there are 5 integer elements 20 bytes of memory is allocated continuously in the memory. (One integer is 4 bytes in size; refer session 2) In the diagram given below each blank section represents an element of the array. 4 bytes

20 bytes Figure 01 – Allocation of memory in an array

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8.1.2 Array elements An array has a unique identifier which is the name of the array. Hence there should be a mechanism to address the array members separately. To access these members individually, the array elements are numbered. Here the first elements always start at 0. Example 8.3: In the example given above, the array contained 5 elements. Hence it can be represented as given below. 0

1

2

3

4

marks Figure 02 – Numbered array elements Each member can be accessed as given below. First element: marks [0] Second: marks [1] Third: marks [2] Fourth: marks [3] Fifth: marks [4] A programmer should be careful in accessing the array elements, since it is somewhat confusing as it always starts from 0 not from 1. In general if an array contains n number of elements the elements are numbered from 0 to n-1. Example 8.4: According to the above example even if the array has 5 elements, it is numbered from marks [0] to marks [4]. Hence if the 3rd element needs to accessed it is marks [2] not marks [3]

8.1.3 A demonstration of the use of an integer array 1. #include 2. #include 3. void main () 4. { 5. clrscr(); 6. int marks[5]; 7. cout<<"Please enter 5 integer values for marks...\n"; 8. for ( int x=0; x<5; x++) { 9. cout<<"marks["<<x<<"]:"; 10. cin>>marks[x]; 11. } 12. cout<<"\nThe 5 values you entered are...\n"; 13. for ( int y=0; y<5; y++) { 14. cout<
Output: Please enter 5 integer values for marks... marks [0] : 25 marks [1] : 85 marks [2] : 78 marks [3] : 19 marks [4] : 56 The 5 values you entered are... 0 : 25 1 : 85 2 : 78 3 : 19 4 : 56 In the above example, an array is declared which can store 5 integer values (line 6). In line 8, a for loop is defined which counts from 0 to 4. Using the first for loop the user is given the opportunity to enter 5 integer values and these values are stored in the array. Using the second for loop all the values that has been stored in the array are displayed. Note: Loops will be used in order to store or display values in arrays. According to the number of elements in the array, the for loop should be correctly initialized and the loop condition should be properly defined.

8.1.4 Initializing Arrays Using the assignment operator (=) values can be initialized to an array just like initializing values to variables. These values should be included inside curly braces and should be separated by commas. Example 8.5: int marks [5] = {34, 89, 67, 45, 50}; 0 marks

1

2

3

4

34 89 67 45 50

Figure 03 –The storage of array elements Elements will be stored in the computer memory in a similar manner to the figure given above. Element that is initialized first will be stored in the first location (0th position) in the array and other elements one after the other according to the way it is initialized.

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An array can be declared by leaving the square brackets empty [ ]. In such a case, the compiler assumes the size of the array is equal to the number of values that has been initialized between the curly braces. Example 8.6: int marks [] = {34, 89, 67, 45, 50}; Since there are 5 values inside the square brackets, the compiler assumes the array has 5 elements and creates an integer array which can store 5 integer values. In addition to the methods given above, elements can be assigned separately to an array. Example 8.7: marks [0] = 34; marks [1] = 89; marks [2+1] = 45; This initialization represents marks [3] In properly initializing an array, the amount of values between braces { } must not be larger or smaller than the number of elements that we declare for the array. If the number of values that has been initialized is larger than the number of elements that has been specified in declaring the array, it will generate compile errors. If the amount of values between braces are smaller than the number of elements, which means if all the array members are not initialized, values of uninitialized members will be set to 0. Example 8.8: marks [5] = {55, 72, 88}; 0 marks

1

2

3

4

55 72 88 0

0

Activity 8.1 – Declaring and initializing array Write a programme which declares a floating point array which can store 5 elements. Initialize the first two elements of the array to 55.5 and 6.8. Let the user input the values for other 3 elements. User input values 55.5

6.8

The programme output should display only the values of each and every number, which has a value more than 50.

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8.2 Multidimensional Arrays So far this session explained only about one dimensional arrays, but it is possible to have arrays of more than one dimension. Each dimension is represented as a subscript in the array. Therefore, a two-dimensional array has two subscripts and a three-dimensional array has three subscripts etc. Arrays can have any number of dimensions, but in writing programmes normally one dimensional and two dimensional arrays are used.

8.2.1. Declaring a two dimensional array In declaring two dimensional arrays, same format and the basic rules apply just like in declaring a one dimensional array, but since there are two dimensions two square braces need to be used to declare the two dimensions. Example 8.9: int array [3][5]; The easiest way to work with the two dimensional array is, visualizing the array as a table with rows and columns. The value declared in the first square braces represent the number of rows and the second square braces represent the number of columns. Just like in one dimensional array, each element starts with 0. int array [3][5] ; 0 1 2 3 4 0 1 2 Figure 04 – Numbered array elements in a two dimensional array

8.2.2 Initializing Multidimensional Arrays Values can be initialized to a multidimensional array just like we initialize values to one dimensional array using the assignment operator. The number of array elements need to be calculated in order to assign values to them. According to the above example the resulting array has 15 elements. (3 x 5). Hence 15 values need to be stored. int array [3][5] = {23,56,5,77,45,2,3,90,65,45,7,11,24,89,10};

In the above initialization it is not an easy task to recognize the values that have been initialized to each position of the array. To improve the readability of the programme as well as for clarity, the values of the elements can be grouped together using curly braces according to the number of rows and columns.

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The above array contains 5 columns. Hence 5 values can be grouped together. The array contains 3 rows; hence 3 value sets should be there. int array [3] [5] = {{23, 56, 5, 77, 45}, {2, 3, 90, 65, 45}, {7, 11, 24, 89, 10}}; Elements of the array will be stored in the computer memory just like in the figure given below.

0 1 2

0

1

2

3

4

23 2 7

56 3 11

5 90 24

77 65 89

45 45 10

Figure 05 –Storage of elements in a two dimensional array There are 3 rows and since each row starts with 0, array elements are numbered from 0 to 2. Since there are 5 columns they are numbered from 0 to 4. Every element can be accessed using both the row number followed by the column number. . Example 8.9: Value 23: marks [0,0] Value 77: marks [0,1] Value 3: marks [0,2] Value 56: marks [1,0] Value 2: marks [2,1] Value 10: marks [2,4] The example given below further explains the use of the two dimensional arrays.

8.2.3 A demonstration of the use of a two dimensional array 1. #include 2. #include 3. void main(){ 4. clrscr(); 5. 6.

const int row = 3; const int col = 5;

7. 8. 9.

int array[row][col] = {{23,56,5,77,45}, {2,3,90,65,45}, {7,11,24,89,10}};

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10. 11. 12. 13. 14. 15. 16. getch(); 17. }

for (int i = 0; i
Output: array [0][0] : 23 array [0][1] : 56 array [0][2] : 5 array [0][3] : 77 array [0][4] : 45 array [1][0] : 2 array [1][1] : 3 array [1][2] : 90 array [1][3] : 65 array [1][4] : 45 array [2][0] : 7 array [2][1] : 11 array [2][2] : 24 array [2][3] : 89 array [2][4] : 10

In creating and accessing one dimensional arrays, a ‘for loop’ is used. Since a two dimensional array has two dimensions, two loops need to be used. In the above example, in line 5 and 6 two constants are assigned for the number of elements in the array. The first for loop in line 10 counts from 0 to 2 which is equal to the number of rows in the array and the second for loop in line 11 counts from 0 to 4 which is equal to the number of columns in the array. When the two for loops are executed, the elements will be printed row by row. The first row of elements will be printed first and then the second row of elements followed by the third row of elements. Note: It is always a good practice to use constants in defining the number of elements in an array. It will help in making modifications to the program easily. For example, if the number of elements in the array needs to be increased or decreased this can be easily achieved by changing only the constants in line 5 and 6 and initializing required elements. The loops need not to be changed. This saves the programmers time a lot specially when modifying large programmes.

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8.3 Arrays as parameters to functions In certain situations arrays needed to be passed as parameters to a function. In passing the array as a parameter to a function, the type of the array, array name and the number of array elements needs to be specified. Example 8.10: int total (int array []) Note: The number of array elements can also be passed to the array as another parameter to the function. This will be discussed in more detail from the example given below.

8.3.1 A demonstration of passing an array as a parameter to a function 1. #include 2. #include 3. int total(int array[],int length); 4. void main(){ 5. clrscr(); 6. 7.

int array_one[]={5,8,7}; int array_two[]={30,5,2,3,4};

8. 9.

cout<<"Total of array one = "<>value[i]; } //Displaying values which are more than 50 cout<<"\nThe values are...\n"; for (int x=0;x<5;x++){ if(value[x]>50) cout<<"array["<<x<<"]:"<
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Activity 8.2 – Answer (a)

#include #include

int maximum(int array[3][4]); void main(){ clrscr(); int array[3][4]={{23, 28, 13,2}, {28, 32, 15, -3}, {19, 27, 20, -7}}; int max_2000=maximum(array); cout<<"Maximum temperature Value is "<<max_2000; getch(); } int maximum(int array[3][4]){ int max=-50; for (int x=0; x<3; x++) for(int y=0;y<4;y++) { if (array[x][y]>max) max=array[x][y]; } return max; } Output: Maximum temperature Value is 32

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Activity 8.2 – Answer (b) #include #include int maximum(unsigned int array[3][4]); void main(){ clrscr(); unsigned int array[3][4]; cout<<"Please enter 12 positive temperature values...\n\n"; for(int i=0;i<3;i++) for(int j=0;j<4;j++){ cout<<"array["<<<"]["<<j<<"]:"; cin>>array[i][j]; } int max_2000=maximum(array); cout<<"\nMaximum temperature Value is "<<max_2000<<endl; getch(); } int maximum(unsigned int array[3][4]){ int max=0; for (int x=0; x<3; x++) for(int y=0;y<4;y++) { if (array[x][y]>max) max=array[x][y]; } return max; }

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Output: Please enter 12 positive temperature values... array [0][0] : 23 array [0][1] : 56 array [0][2] : 5 array [0][3] : 77 array [1][0] : 2 array [1][1] : 3 array [1][2] : 90 array [1][3] : 65 array [2][0] : 7 array [2][1] : 11 array [2][2] : 24 array [2][3] : 89 Maximum temperature Value is 90

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Session 9 Pointers Content Objectives Introduction 9.1 What is a pointer? 9.1.1 Declaring Pointers 9.1.2 Initializing Pointers 9.1.3 A demonstration on the use of pointers 9.1.4 A demonstration on assigning values to variables using pointers 9. 2 Pointers and arrays 9.2.1 Calculations using pointers 9.2.2 A demonstration on the use of pointers to assign members to an array 9.3 Pointers to pointers 9.4 Pointers to functions 9.4.1 A demonstration on the use of pointers in functions Summary

Objectives After reading this lesson you should be able to: ¾ ¾ ¾ ¾

Understand what pointers are Declare, initialise and use pointers Declare pointers to functions and to arrays Declare a pointer to another pointer

Introduction In working with variables, regardless of the physical location of the data within the memory, we simply use its identifier whenever we want to refer to the content of the variable. Using pointers it is possible to directly manipulate with computer memory. Hence pointers can be considered as one of the most powerful programming techniques available in C++. To understand pointers, it is vital to have knowledge about computer memory. A computer’s memory consists of thousands of sequential storage locations and each location is identified by a unique memory address. The memory addresses in a given computer range from 0 to a maximum value. The maximum value depends on the amount of memory installed in a given computer. Using pointers it is possible to manipulate directly with these memory addresses. This session explains how to manipulate data using pointers.

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Working with pointers can be sometimes confusing. Pointer bugs can crash in random ways that makes it more difficult to correct them. Hence, in order to work with pointers you should have a clear understanding of how to manipulate them correctly.

9.1 What is a Pointer? A pointer is a reference whose value refers or point directly to another value stored elsewhere in the computer memory. Pointers do not store a value directly just like normal variables store values. Instead, a pointer stores a reference of another value. A pointer contains the address of a data construct. Therefore, pointers are of the same size regardless of what they are pointing to.

9.1.1 Declaring Pointers A pointer must be declared before it is used. The general format of declaring a pointer is: data_type *pointer_name; In declaring pointers, the pointer type needs to be declared first (int, char, float etc), followed by the name of the pointer. Before the pointer name, an asterisk (*) is used to denote that this is a pointer and not a variable. This asterisk mark is also called the ‘value of operator’. Example 9.1: int *p1; The integer type pointer declared above is named, ‘p1’ Number of pointers and variables can also be declared at the same time. Example 9.2: int *p1, *p2, result;

9.1.2 Initializing Pointers A pointer cannot perform any task until it is initialized. Until a pointer holds the address of a variable, it isn't useful. Here the ampersand (&) operator is used to assign the address on a variable to the pointer. The ampersand mark is also called the ‘address operator’. Example 9.3 : int *p1, result; result =10; p1 = &result; In the example given above, first an integer type pointer (*p1) and a variable called ‘result’ are declared. Then the variable is assigned the value 10 and the address of the variable (&result) is assigned to the pointer p1. This is further explained using the diagram given below using the concept how the pointers are arranged in the computer memory. 103

0 1 2 3 : : : 42642281 42642282 42642283 42642284

10 : : :

Variable ‘value’

3

‘p1’ pointer

Computer Memory Figure 9.1- How pointers are arranged in the computer memory According to figure 9.1, when the variable is declared, it is assigned the memory location 3, and when the pointer is declared it is assigned the memory location 42642282 (Also refer the example 9.3). When the variable is initialized to 10, the value 10 is stored in that memory location assigned to the variable (memory address 3). After that when the address of the variable is assigned to the pointer using the address of (&) operator, the pointer called p1 points to the variable called ‘result’. The pointer points to the variable by storing the address of the variable (address 3) in the pointer’s memory location, which is 42642282. ¾ The content of the variable result is 10. ¾ The memory address of the variable result is 3. ¾ The content of the pointer p1 is 3 because it has stored the address of the variable result. Note: The memory addresses that are used in figure 9.1 are just arbitrary assumption values.

9.1.3 A demonstration on the use of pointers 1. #include 2. #include 3. void main () 4. { 5. clrscr(); 6. 7. 8.

int var = 1; int *ptr; ptr = &var;//Initialize ptr to point to var

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9. 10. 11.

cout<<"Content of the variable (Direct Access) : "<
12. 13. 14.

//Accessing memory address of the variable in two ways cout<<"Memory address of the variable (using the variable): "<<&var<<endl; cout<<"Memory address of the variable (using the pointer) : "<
15. getch(); 16. } Output: Content of the variable (Direct Access) : 1 Content of the variable (Indirect Access): 1 Memory address of the variable (using the variable): 0x8fc7fff4 Memory address of the variable (using the pointer) : 0x8fc7fff4 In the programme given above, in line 6 an integer variable called var is declared and it is initialized to 1. In line 7, a pointer of type int is declared and named as ‘ptr’. In line 8, the pointer ptr is assigned the address of var using the address of operator (&). The rest of the program prints the values and addresses of the variable and the pointer. Line 9 prints the value of var just like printing a value stored in a normal variable and it is called ‘direct access’ because the content of a variable is accessed using the variable name. In line 10, it prints the value stored in var, pointed by ptr (Using the value of operator *) and this is called ‘indirect access’ because the content of a variable is accessed using a pointer. In this program, the value is equal to 1. Line 13 prints the address of var using the address-of operator (&). This is equal to the value printed by line 14 using the pointer variable ptr because the value that is stored in the pointer is the address of the variable. A pointer name without the ampersand operator accesses the pointer value itself, which is the address of the variable pointed to. ¾ *ptr and var both refer to the contents of var (that is, whatever value the program has stored in the variable). ¾ ptr and &var refer to the address of var. Note: The pointer should be of the same type as the variable that needs to be pointed. int *p1- This pointer can point only to an integer value Char *p2- This pointer can point only to an char value Values can also be assigned to variables using pointers. The example given below shows how pointers can be used to assign values to variables.

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9.1.4 A demonstration on assigning values to variables using pointers 1. #include 2. #include 3. void main () 4. { 5. clrscr(); 6. 7.

float height, length; float *h, *l;

8. 9.

height=5.5; length=8.3;

10. 11.

h= &height; l= &length;

12. 13. 14. 15. 16. 17.

cout<<"Height is "<<*h<<endl; cout<<"Length is "<<*l<<endl; *h = 10.55; *l = 18.33; cout<<"\nNew height is "<
18. getch(); 19. } Output: Height is 5.5 Length is 8.3 New height is 10.55 New length is 18.33 In the example given above, the variables ‘height’ and ‘length’ are first assigned to 5.5 and 8.3 respectively (line 8 and 9). Then using the two pointers ‘h’ and ‘l’, different values are reassigned to the variables. (line14 and 15). When the pointer is used with the asterisk (*), it always refers to the content of the variable that the pointer refers to. Hence values can be assigned to the variables using the pointers. After assigning values using pointers, the content of the variables have been changed to 10.55 and to 18.33. This is evident from the programme output. (refer line 16 and 17)

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It is possible to assign more than one pointer which points to a same variable. Example 9.4: int marks=20; int *p1, *p2; p1=&marks; p2=&marks; marks

Memory address: 456788

20

p1 456788

456788

p2

Figure 9.2- Two pointers, pointing to a same variable In figure 9.2 both pointers (p1and p2) hold the memory address of the variable marks.

9. 2 Pointers and arrays Array elements can also be accessed using pointers. When an array is assigned to a pointer it points to the first element of the array. Example 9.5: int marks [10]; int *p; p=marks; The array can also be assigned to the pointer as p = &marks [0];

9.2.1 Calculations using pointers Meaningful arithmetic operations can be done using pointers, but only addition and subtractions are allowed. Hence this mechanism can be used in assigning values to an array and to access these members separately. The members of an array can be accessed in different ways using pointers. Check the example given below.

9.2.2 A demonstration on the use of pointers to assign members to an array 1. #include 2. #include 3. void main () 4. { 5. clrscr();

107

6. 7. 8.

int marks[6]; int *p; p=marks;

9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

*p=45; //allocating marks[0]=45 p++; *p=55; //allocating marks[1]=55 p=&marks[2]; *p=65; //allocating marks[2]=65 p=marks; *(p+3)=75; //allocating marks[3]=75 marks[4]=85; //allocating marks[4]=85 p=marks; p=p+5; *p=95; //allocating marks[5]=95

20. 21. 22. 23.

for (int x=0;x<=5;x++) { cout<<marks[x]<<"\n"; }

24. getch(); 25. } Output: 45 55 65 75 85 95

0 marks

1

2

3

4

5

45 55 65 75 85 95 P

(P+3)

P=P+5

P++ P=&marks[2]

Figure 9.3 – Assigning values to an array using a pointer Since a pointer is first pointed to the first element of the array, a value to the first element can be easily assigned (line 9). Another simple way to access an array element is the use of the ++ operator. Using the ++ operator, 55 is allocated as the second element of the array. (line 10 and 11) Then a value needs to be assigned to the next position of the array, which is marks [2.] Since the use of the ‘address of’ operator (&), the pointer points to the address of the element marks [2] (line 12) and the value 65 is allocated to that position. Refer line 13 in the above programme.

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As the next step in line 14 the array is again assigned to the pointer, which means the pointer points to the first element of the array again (line 14). Then straight away by adding 3 to the pointer it points to the 4th position on the array and 75 is allocated to that position. (line 15 and 16) This can be done in another similar manner which is shown in line 17,18 and 19. After assigning the array again to the pointer, (line 17) 5 is added to the pointer which makes it point to the 5th position of the array and 95 is assigned to the position. In addition to assigning values to an array using pointers, values in an array can also be accessed using pointers. Values can also be subtracted from the pointer and can be used to access elements in an array. Note: In increasing or decreasing the value that a pointer points to, always use parenthesis () to make sure that the addition and subtraction is applied to the pointer and not to its value. *(p-2) //correct *p-2 //incorrect

Activity 9.1 – Storing and accessing elements of an array using pointers Declare the integer array given below, which can hold 5 elements. int salary[5]; (a) Assign the values given below to the array using a pointer. 32700, 15000, 7500, 28000, 10000 Display the above values using a loop. (refer example 9.2.2) Hint: You can use one or more methods that were discussed in example 9.2.2, to assign values to the array. (b) Modify the above programme in order to display the values that are stored in the array using a pointer and a loop (either a while loop or a for loop)

9.3 Pointers to pointers A pointer can be pointed not only to a pointer, it also can point to another pointer. Example 9.6: char letter=’a’; char *p1,*p2; p1=&letter; p2=&p1;

109

letter a

p1 23

p2 3876

234

3876

10100

Figure 9.4 – Pointer that points to another pointer

9.4 Pointers to functions Many operations can be performed using pointers and functions. A pointer to a function holds the starting address of a function. Hence, this is a more flexible way of calling a function. This feature can be used to point to different functions depending on the program conditions. Here also the pointer needs to be declared before it is been used. The general format of the declaration is: data_type (*pointer_to_function)(parameter1, parameter2, …); According to the above format, type of the pointer should be declared first, followed by the pointer name. Next, the parameter list of the function needs to be declared enclosed between parentheses. The data type of the pointer and the parameter list should also match the return type and the parameter list of the function or functions that it points to. Example 9.7:

int (*ptr)(int x, int y); void (*p)(float y, float z);

9.4.1 A demonstration on the use of pointers in functions 1. #include 2. #include 3. float area(float radius); //Prototype of the function 4. float (*p)(float radius); //Declaration of the pointer 5. void main(){ 6. clrscr(); 7. 8. 9.

p = area;//Initilising pointer 'p' to point to function 'area' float answer=p(8.1); //Calling the function using the pointer cout<<"Area of the circle is "<
10. getch(); 11. }

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12. //Function Definition 13. float area(float radius) 14. { 15. return 3.14159*radius*radius; 16. } Output:

Area of the circle is 206119736

The programme given above calculates the area of a circle. First, the prototype of the function is declared (refer line 3). In line 4 the pointer is declared and it is initialized to the function in line 7. After the function call in line 8, the area of the circle is displayed using the pointer.

Activity 9.2 – Using a pointer to a function to call different functions depending on the program conditions

Create the following menu. ----------------Menu----------1.Calculating the factorial value 2.Calculating the sqaure value 3.Exit programme Write a programme, which gives the user the opportunity to enter either option. When the user selects option 1, your programme should request the user to enter an integer value. Then the factorial should be calculated and answer should be displayed according to the value that the user entered. Similarly, when the user selects option 2, the square value should be calculated and the answer displayed according to the value that the user entered. Use a pointer to call different functions depending on the option that user has entered. When the user selects option 3, your programme should exit.

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Summary ¾ Pointers are variables that point to an area in memory. A pointer is defined by adding an asterisk (*) in front of a variable name. The asterisk mark is also called the ‘value of operator’. ¾ A pointer needs to be assigned before it is been used. The ampersand (&) operator is used to assign the address on a variable to the pointer. The ampersand mark is also called the ‘address of operator’. ¾ ‘*pointer_name’ and ‘variable_name’ both refer to the contents of the variable whereas ‘pointer_name’ and ‘&variable_name’ refer to the address of the variable. ¾ It is possible to assign more than one pointer which points to the same variable. ¾ Arithmetic operations addition and subtraction can be performed with pointers. ¾ It is possible to store and access elements of an array using pointers. ¾ Many operations can be performed using pointers, which points to functions.

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Session 9 – Answers

Activity 9.1 – Answer (a) #include #include void main() { clrscr(); int salary[5]; int *p; p=salary; *p=32700; //Assigning salary[0]=32700 p++; *p=15000; //Assigning salary[1]=15000 p=salary; *(p+2)=7500; //Assigning salary[2]=7500 p=&salary[3]; *p=28000; //Assigning salary[3]=28000 p=salary; p=p+4; //Assigning salary[4]=10000 *p=10000; cout<<"Values of the array:\n\n"; for(int x=0;x<5;x++){ cout<<"salary["[x]<<"]="<<salary[x]<<endl; } getch(); } Output: Values of the array: Salary[0] = 32700; Salary[1] = 15000; Salary[2] = 7500; Salary[3] = 28000; Salary[4] = 10000;

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Activity 9.1 – Answer (b)

#include #include void main() { clrscr(); int salary[5]; int *p; p=salary; *p=32700; //Assigning salary[0]=32700 p++; *p=15000; //Assigning salary[1]=15000 p=salary; *(p+2)=7500; //Assigning salary[2]=7500 p=&salary[3]; *p=28000; //Assigning salary[3]=28000 p=salary; p=p+4; //Assigning salary[4]=10000 *p=10000; p=salary; //Pointer points to the first element of the array cout<<"Values of the array:\n\n"; for(int x=0;x<5;x++){ cout<<"Salary["<<x<<"]="<<*p<<endl; p=p+1; } getch(); } Output: Values of the array: Salary[0] = 32700; Salary[1] = 15000; Salary[2] = 7500; Salary[3] = 28000; Salary[4] = 10000;

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Activity 9.2 – Answer #include #include #include<stdlib.h> int factorial (int x); int square(int y); int (*ptr)(int); void main() { clrscr(); int option,value,answer; cout<<"---------------Menu--------------\n"; cout<<"1.Calculating the factorial value;\n"; cout<<"2.Calculating the sqaure value\n"; cout<<"3.Exit programme\n\n"; cout<<"Enter your option:"; cin>>option; if(option!=3){ cout<<"Enter an integer value:"; cin>>value; if (option == 1){ ptr = factorial; answer=ptr(value); cout<<"Factorial of "<
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int factorial (int x) { int fact=1; for(int a=1;a<=x;a++){ fact=fact*a; } return fact; } int square(int y) { return y*y; } Output: ---------------Menu-------------1. Calculating the factorial value 2. Calculating the sqaure value 3. Exit programme Enter your option: 2 Enter an integer value: 10 Square of 10 is 100

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Session 10 More on Functions and Strings Content Objectives Introduction 10.1 Local and Global variables 10.1.1 A demonstration on the use of local and global variables 10.2 Arguments passed by value and by reference 10.2.1 A comparison on the use of passing by value and reference 10.3 Recursion 10.3.1 A demonstration on ‘Recursion’ 10.4 String Functions 10.4.1 A demonstration on the use ‘char arrays’ 10.4.2 A demonstration on the use of ‘gets’ function 10.5 C++ String Functions 10.5.1 A demonstration on the use of ‘strcmp’ function Summary

Objectives After reading this lesson you should be able to: ¾ Declare local and global variables ¾ Understand the difference between passing arguments to functions ‘by value’ and ‘by reference’ ¾ Manipulate with ‘strings’ using string functions

Introduction In session 7 we learnt the basics of functions, how they are declared, defined, and executed. This session covers more aspects of functions. First, it introduces local and global variables, which is an important aspect even in ‘Object Oriented Programming’, which will be covered in the sessions to come. In addition, this session addresses the methods that arguments can be passed into a function as well as the property called ‘recursion’ which is used in C++ programming.

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The concepts and examples that were discussed in the previous sessions were based on manipulating data, which hold numerical values. In addition, we learnt that by using character variables only a single letter, number, or a symbol could be stored. This is not sufficient in programming. Hence the concepts of ‘strings’ can be introduced, which allow the user to store not only a single character but to store a series of non-numerical characters. C++ has different methods to perform operations with ‘strings’ as well as a powerful string class library where different functions are defined in order to manipulate with them. This session covers some of these functions as well.

10.1 Local and Global variables Local variables are variables that are declared and defined inside the body of the function. The variables can be used to store values inside the function, as they exist only locally within the function itself. These kinds of variables said to have a ‘local scope’, which means the scope of local variables is limited to the same block level in which they are declared. Variables declared outside the body of any other function is considered as global variables and can be accessed inside any function in the programme. These variables said to have ‘global scope’. Note 1: If a function has a variable with the same name as a global variable, the name refers to the local variable (not the global variable) when used within the function. Note 2: Un-initialized global variables are automatically initialized to zero. Generally, the lifetime of a variable is limited to its scope. Global variables last for the duration of programme execution, while local variables are created when their scope is entered and destroyed when the programme exit its scope. The memory space for global variables is reserved prior to commencing of the programme execution, whereas memory space for local variables is allocated only for the time that the variables are being used.

10.1.1 A demonstration on the use of local and global variables 1. #include 2. #include 3. void addFunction(); //function prototype 4. int x = 5, y = 7; //declaration of global variables 5. void main () 6. { 7. clrscr(); 8. cout << "Total (inside main function): " << x+y<< "\n\n"; 9. addFunction();

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10. getch(); 11. } 12. void addFunction() 13. { 14. int y = 10; 15. int total; 16. total=x+y; 17. cout << "Total (inside add function): " <
10.2 Arguments passed by value and by reference There are two ways to pass arguments to a function. That is passing arguments by its value and by its reference. Most of the examples that were discussed in session 7 are of arguments that are passed by its value. In considering passing arguments by value during the function call, what is passed to the function are copies of their values and not the actual variables. Hence changes that have been made to the function arguments inside the function do not affect the variables that have been declared outside the function. Example 10.1:

int x=2, y=10; addition(x,y); //function call 2

10

int addition(int value1,int value2) {

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result = value1+value2; return result; } Example 10.1 shows part of a programme. During the function call, values 2 and 10 are passed into the function arguments value1 and value2 respectively. If we make changes to the function arguments (value1 and value2) inside the function, it does not affect the variables x and y which are defined outside the function because x and y variables are not passed into the function but only their values are passed. In passing values as references to a function, ampersand (&) sign is used before the function arguments that need to be passed as references. When passing by reference, the variable itself is passed into the function and not the copies of their values. Hence all the changes that have been made to the function arguments inside the function straight away affect the variables that have been passed to the function. Check the example given below. Example 10.2: int x=2, y=10; counter ( x, y);

void counter(int &value1,int &value2) { ++value1; ++value2; } In the example given above, the ampersand (&) mark has been used before the function arguments (&value1 and &value2). It specifies that the arguments need to be passed into the function by reference instead of by value. Inside the function, both function arguments ‘value1’ and ‘value2’ has been incremented. Those increments affect the variables x and y which is defined outside the function. The programmes given below as an example clarify these concepts.

10.2.1 A comparison on the use of passing by value and reference Passing by Value

Passing by Reference 17. #include 18. #include

1. #include 2. #include 3. void counter(int value2);

19. void counter(int &value2);

value1,int

20. void main () 21. {

4. void main () 5. {

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&value1,int

6. clrscr();

22. clrscr();

7. int x=2, y=10; 8. counter(x,y); 9. cout<<"x="<<x<<"\ny="<
23. int x=2, y=10; 24. counter(x,y); 25. cout<<"x="<<x<<"\ny="<
10. getch(); 11. }

26. getch(); 27. }

12. void counter (int value1, int value2) 13. { 14. ++value1; 15. ++value2; 16. }

28. void counter &value2) 29. { 30. ++value1; 31. ++value2; 32. }

Output:

Output:

x=2 y=10

x=3 y=11

(int

&value1

,int

In the above example named ‘passing by value’, the values of x and y doesn’t change even though the function is being called (line 8). This is evident from the programme output. The reason is that only the copies of x and y are passed into the function. Hence, it is not possible to manipulate the value of an external variable from inside a function. In the next example where the arguments are passed by it’s reference when the function ‘counter’ is called, value1 and value2 become references to x and y variables. Hence inside the function the changes that have been made to value1 and value2 affect x and y. Both x and y have been incremented and values of x and y variables increased to 3 and 11 respectively.

10.3 Recursion Recursion means the ability that the function has, which could call itself. In the function definition there is a point where the function calls to that very same function and repeats the same code. In programming this method is useful in many tasks like sorting and calculating. A recursive function should possess two main characteristics. 1. It should have an ending point – If the function doesn’t have an end point it will be calling itself again and again and will behave like a never ending loop. Hence, there should be a condition where the function should exit from the recursion. 2. It must make the problem simpler – The problem should become smaller on each recursion 121

10.3.1 A demonstration on ‘Recursion’ 1. #include 2. #include 3. void main() 4. { 5. clrscr(); 6. unsigned int factorial(unsigned int value); 7. int number, result; 8. cout << "Enter an Integer number between 0 and 10:"; 9. cin >> number; 10. 11. 12. 13.

if(number>=0 && number<=10){ result = factorial(number); cout << "Factorial of "<
14. 15. 16.

else{ cout<<"Illegal number!\n\n"; }

17. getch(); 18. } 19. unsigned int factorial (unsigned int value) 20. { 21. if(value==0) 22. return 1; 23. else 24. return (value*factorial(value-1)); 25. } Output: Enter an Integer number between 0 and 10: 3 Factorial of 3 is 6 The programme given above calculates the factorial of a given value. As an example, the factorial value of 3 has been calculated. (3! =3*2*1=6). In line 10, it checks whether the number that the user has entered is between 0 and 10. If the value is in the specified range the programme calls the function called ‘factorial’ (line 11). If not, it returns an error message. (line 15)

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When the programme call the function ‘factorial’ inside the function definition, it first executes the else statement since the value that the user has entered (3) is not equal to 0 (Refer line 23 & 24). When the else statement is executed, it becomes (3*factorial (3-1)), which means the function factorial is called again by passing the value 2 as the argument into the function. Hence the problem is getting simpler as the factorial of 2 needs to be calculated now. In the next iteration the factorial of 1 needs to be calculated. In the last recursion the value becomes 0 since factorial (1-1) becomes factorial 0. Then the ‘if statement’ executes and the function return back to the main method. (line 21 & 22) The above programme has 2 main characteristics that have been mentioned earlier. It has an ending point where the function exits when the value becomes 0 and it also makes the problems simpler in each iteration. Note: Refer session 7 ‘Activity 7.1-Answer’. The factorial value of a given number is calculated using a ‘for loop’. In 10.3.1 the recursive method is used to calculate the factorial value, which is a much simpler method.

Activity 10.1 – The use of recursion with arrays

Write a programme, which declares an integer array, which can hold 5 elements. Let the user enter 5 values to the array from the keyboard. Then the programme should calculate and display the sum of the values of the elements using a recursive function.

10.4 String Functions Variables that can store non-numerical values and values that are longer than one single character are known as strings. Strings are of series of characters. Hence the concepts of arrays can be used in order to create strings. Example 10.3: char name []= {‘O’, ’p’, ’e’, ’n’, ’ ’, ’U’, ’n’, ’i’, ’v’, ‘e’, ’r’, ’s’, ’i’, ’t’, ’y’,’\0’ } The arrangement of the char array can be represented as given below.

name

0

1

2

3

O

p

e

n

4

5

6

7

8

9

10

11

12

13

14

15

U

n

i

v

e

r

s

i

t

y

\0

Figure 01 – The storage of char array elements The declaration and initialization of a char array is similar to any other array except that all the elements in a char array needs to be enclosed within single quotes. If an element or a collection of elements (words) needs to be separated, a space between those words 123

should be enclosed within single quotes. The last element of the array ‘\0’ is a null character and C++ functions recognize it as a terminator for C++ strings. Above initialization of elements is time consuming and prone to errors since several single quotes needs to be specified. Hence C++ provides easier way to declare elements in a char array by including the string inside double quotes. (Curly braces need not to be included) Example 10.4: char name [] =”Open University”;

10.4.1 A demonstration on the use ‘char arrays’ 1. #include 2. #include 3. void main(){ 4. clrscr(); 5. 6.

char name[100]; char greeting[]="Welcome to Department of ";

7. 8. 9.

cout<<" Please enter the name of your department:"; cin>>name; cout<
10. getch(); 11. } Output: Please enter the name of your department: Mechanical Engineering Welcome to Department of Mechanical In the above example in line 5, an array called ‘name’ is defined which can hold 100 elements. In line 6 another array is defined and a string message ‘Welcome to Department of’ is initialized to the array. When the user enters a department name, the programme should display a greeting followed by the name of that department. When observing the output carefully, it is evident that part of the programme is not working properly. The welcome message is displayed correctly but only the first part of the word ‘Mechanical’ is displayed even though the user had entered two words which is ‘Mechanical Engineering’ The reason for this is since the user has entered a space in order to separate the two words, the cin function assumes that it’s the end of the string when it comes to the space after the first word. Therefore the programme displays only the first word that the user entered.

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To avoid this problem C++ library has a separate function called ‘gets’ function, which is defined in the <stdio.h> header file. The general format of the gets functions is: gets (array_name)

10.4.2 A demonstration on the use of ‘gets’ function 1. #include 2. #include 3. #include<stdio.h> 4. void main(){ 5. clrscr(); 6. char name[100]; 7. char greeting[]="Welcome to Department of "; 8. cout<<"Please enter the name of your department:"; 9. gets(name); 10. cout<>get(array name, maximum_charaters_to_get) Example 10.5: char name [100]; cin>>get (name, 99) According example 10.5, ‘name’ is the name of the array and the maximum characters that the array can hold is 99, because the last element needs to be allocated for the null character (‘\0’).

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10.5 C++ String Functions In addition to the above functions, C++ provides more sophisticated methods in order to manipulate with strings. For this purpose the C++ library has a standard string class. In order to use the functions provide with it, the standard header file called the ‘string’ header file needs to be included in the programme. Some of the functions provided by the string class are given below. Function Name strlen(string) strcat(string1,string2) strcpy (string1,string2) Strstr (string1, string2) strcmp(string1,string2) stricmp(string1,string2)

Operation Returns the number of characters (length) in a string Concatenates string2 to the end of string1 Copy a string (Copy string2 to string1) Find the first occurrence of string2 in string1 Compare string2 with string1 Compare string2 with string1 without regard to case

Table 01 – String-Handling Functions

10.5.1 A demonstration on the use of ‘strcmp’ function 1. 2. 3. 4.

#include #include #include<stdio.h> #include<string.h>

5. void main(){ 6. clrscr(); 7. 8. 9.

char password[10]; cout<<"Please enter your password:"; gets(password);

10. 11. 12. 13.

if(!strcmp(password,"ousl 2007")) cout<<"Correct password!"; else cout<<"Incorrect password!";

14. getch(); 15. } Output: Please enter your password: OUSL 2007 Incorrect password!

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Programme 10.4.1 let the user to enter a password as the input. If the password that the user has entered is correct, the programme displays a message indicating that the password is correct and if the password is incorrect it returns an error message indicating that the password is incorrect. In the above example, ‘gets’ function is used to take the user input. (line 9). When the user enters a string, the programme compares the two strings. They are the stored password (ousl 2007) and the password that the user has entered. (OUSL 2007). Refer line10. Here, a not sign (!) is used before the ‘strcmp’ function because if scrcpm() function becomes true, it returns 0 and if it becomes false it returns 1. (Normally other functions we have leant so far operate the other way around which returns 1 if the statement is true and 0 when the statement becomes false). Hence it is advised to use the not sign (!) in order to get the correct output. According to the programme, even though correct characters have been entered as the password, it gives the output ‘Incorrect password!’ because the function checks even for the upper and lower case letters. Note: ‘String’ header file is included in the programme since ‘strcmp’ function is been used and ‘stdio’ header file has been included since the ‘gets’ function is been used.

Activity 10.2 – Understanding string handling functions Write a programme, which asks the user to enter a name of a book and a description about the book. The name of the book should be more than 2 characters long and the description should be more than 20 characters long. If the user’s input doesn’t meet the above requirements, an error message should be displayed indicating that the information entered is not sufficient. If the user enters correct information, it should be displayed back to the user.

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Summary ¾ Local variables are variables that are declared and defined inside the body of the function, which has a ‘local scope’. ¾ Global variables are variables that are declared and define outside the body of the function, which has a ‘global scope’. ¾ There are two ways to pass arguments to a function. That is passing arguments by its value and by its reference. ¾ Recursion means the ability that the function has, which can call itself. In programming this is useful in order to achieve many tasks. ¾ Variables that can store non-numerical values and are longer than one single character are known as strings. ¾ C++ string library provides more sophisticated methods in order to manipulate with strings. Some of the string handling functions are strlen, strcpy, strcmp, strcat etc

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Session 10 – Answers Activity 10.1 – Answer #include #include int sum(int array[],int first,int last); void main() { clrscr(); int num_array[5]; cout << "Please enter 5 numbers:"<<endl; for(int x=0; x<5;x++) cin>>num_array[x]; cout<<"\nThe numbers you entered are: "<<endl; for(x = 0;x<5;x++) cout<
Activity 10.2 – Answer #include #include #include<stdio.h> #include<string.h> void main(){ clrscr(); char book[50]; char desc[100]; cout<<"Enter a name of a book:"; gets(book); cout<<"Enter a description about the book:"; gets(desc); //int temp=strlen(subject); if ((strlen(desc)>20)&&(strlen(book)>2)){ cout<<"\nBook Name : "<
Output 2: Enter a name of a book: Mechantronics Enter a description about the book: An introductory book Information you entered is not Sufficient! 130